Added autosaving of the current map. Autosaving happens in intervals when the map is changed. It will not overwrite the current map, but rather create new files, just like backups. Autosaving interval and number of files can be configured in the "Recovery" tab of the preferences. Autosaving can also be disabled there (not recommended). Autosaves will not have their nodes built for performance reason.

Point Thing at Cursor: check for a thing's fixedrotation rather than its category's arrow setting (#957)

Fixed a problem where not selected geometry and things could not be dragged when the "don't move selection if any part of it is outside of map boundary" option was enabled

(Text labels are removed because of performance issues)

Added action to change the index of linedefs, things, sectors, and vertices. Can be accessed through a shortcut (not bound by default) or the menu of the respective mode (#903)

Fixed a regression where editing map elements did not preserve the selection order, but used the index order instead. Fixes #791

- editing a highlighted, not selected map element will deselect other selected map elements, then start editing the highlighted map element
- dragging a highlighted, not selected map element will deselect other selected map elements, then start dragging the highlighted map element
- dragging a single map element will keep its selection state. I.e. dragging a selected map element will not deselect it after dragging anymore
  - dragging a highlighted, not selected thing will not select it after dragging
- dragging a highlighted, not selected sector, while other sectors are selected, will only drag the highlighted sector, and not the selected sector (and deselect the selected sectors)

Added map scripting capabilities to UDB (#656). Documentation at https://biwa.github.io/udbscript-docs/

Editing modes: fixed some crashes related to undoing/redoing while objects with associations were highlighted

Improved associations and event lines. Refactorings to make the whole thing more sensible (hopefully). Options to display labels on event lines (can be configured in Preferences -> Editing).

Things Mode: performing the smart grid transform action will now set the grid origin to the selected or highlighted thing
Sectors Mode: performing the smart grid transform action will now reset the grid transform

- Added option to enable additive paint selecting without holding shift independently from regular additive selecting

* Mouse selection threshold

* Cleanup

* Fix selection bug

Fixed: inheritance from game configuration for dynamic lights; Fixed: visual representation of inherited lights (reported by Nash); Fixed: inherited thing arguments from game configuration; Added: //$ClearArgs for clearing inherited arguments.

* A direct tag-to-tag relationship can now be established between two things, which allows event lines to be properly setup between them. This is intended for interpolation and patrol specials which are linked via a shared tag, instead of an argument. A POSITIVE value represents the parent thing, where a NEGATIVE value represents the child thing.
* Added interpolation and patrol point specials to the persistent event line processing

Updated, Textures Browser: texture name length is now taken into account when calculating the width of texture items.
Internal: moved thing helper shapes creation logic from ThingsMode to LinksCollector.

Added, Things mode, Visual mode: added the ability to specify minimum/maximum argument range hint shapes using special DECORATE comments and Game Configuration properties (loosely based on range finder patch by Xabis).
Updated documentation ("Game Configuration - Action Argument Settings" and "DECORATE keys" pages).

Fixed, Script Editor: MD5 hash of text files stored in PK3 was calculated incorrectly, resulting in false warning messages when saving.

Added, Errors and Warnings window: most of warnings/errors related to (G)ZDoom text lump parsing can now be double-clicked to show warning/error source in the Script Editor.
Fixed: some map format conversion errors were never displayed, because errors list was cleared after performing map conversion.
Fixed: 3d floor indicators in 2D modes were not updated after leaving Visual mode.
Fixed: some UDMF-only interface buttons were never removed after converting map format from UDMF.

Fixed, Things mode: fixed a crash when deleting Light/Ambient Sound things when "Show Dynamic Light Radii" / "Show Ambient Sound Radii" settings were enabled.
Fixed: WAD lump index was not appended to lump name when reporting errors during ZDoom text lumps parsing.

Updated ZDoom_DECORATE.cfg.
Updated documentation ("Game Configuration - Sectors Settings" page).

Added, Things mode: sound radii are now shown for "Custom Ambient Sound" and "Custom Ambient Sound (no gravity)" things.

Added, Things mode: minimum/maximum sound radii can now be displayed for ZDoom's Ambient Sound things.
Added, Things mode: added "Show Light Radii" and "Show Sound Radii" main toolbar and View menu buttons.
Fixed, Action arguments control: invisible splitter between args1-3 and args4-5 is no longer draggable.
Updated ZDoom ACC (SetTranslation).
Updated ZDoom_ACS.cfg (SetTranslation).

Changed, Vertices/Linedefs/Sectors/Things modes: selected map element is no longer deselected after accepting Edit window when it was the only selected map element when the Edit window was opening.

Fixed, Things mode: thing selection labels must be updated when performing undo/redo.
Fixed another case of invalid sectors being created after dragging map elements when using "Merge Dragged Geometry" and "Replace with Dragged Geometry" drag modes.

Merged "Toggle models, dynamic lights and fog rendering" and "Toggle Geometry Effects" actions into "Toggle Enhanced Rendering Effects" action.
Removed "Dynamic light size" and "Dynamic light intensity" settings.
Updated documentation ("Rendering toolbar" page).

Added, DECORATE: added "//$ArgNRenderStyle" special comment. It allows to specify a rendering shape to display the value of given argument. Supported values are "circle" and "rectangle".
Added, DECORATE: added "//$ArgNRenderColor" special comment. It allows to specify a color used by the rendering shape.
Updated documentation.

Added, Visual mode: added support for FLATSPRITE, ROLLSPRITE, WALLSPRITE and DONTFLIP sprite rendering flags. Removed the older GLOOME-specific implementation.
Changed, "Align Things to Nearest Linedef" action: the action can now also align things with FLATSPRITE and WALLSPRITE flags (previously only things with attached models were aligned).
Changed, "Align Things to Nearest Linedef" action: the action can now align things to the middle part of double-sided linedef, if it has a middle texture assigned. 

Fixed: parts of UniFileds.UniValuesMatch() logic were inverted. In some cases this resulted in incorrect behavior of "Select Similar" action in UDMF map format.
Fixed, UDMF: alpha should be ignored when applying sector fade/light color gradients.
Ported eevee's fix for incorrect sector geometry occasionally created after dragging map elements (more info: https://github.com/sirjuddington/SLADE/issues/542).