- target_sources from correct directory
- enable_language must be used in add_executable directory

2.2.9 prep

See merge request !1499

Stop using metatables with light userdata

See merge request !1495

Update URL on the addon screen

See merge request !1489

Fix MusicChange hook not returning some values correctly

See merge request !1496

This establishes (near) parity of source code file lists
between the Makefile and CMakeLists.txt

To make that change I messed around CMakeLists.txt a bit.
It now uses target_sources and target_compile_definitions.
I also removed some MSVC stuff since we don't actually
care about MSVC--it made things easier.

CMake minimum version 3.0 -> 3.13 for target_sources.

- Quotes were not removed by ECHO.
- DEL would print an error on nonexistent file.
- MD would do this plus return a nonzero exit code.

Some key points for programmers:
- Source code files are mostly listed in a 'Sourcefile'.
  So you no longer directly edit the object list. There
  can be multiple Sourcefiles and they can even live in
  subdirectories--the directory name will be prepended to
  every filename in the list. Of course, the Makefile
  still needs to be edited to read from each Sourcefile.
- Different rules are no longer required for source code
  files that live in subdirectories (such as sdl/ or
  hardware/). Subdirectories Just Work so go ham!

In addition to those points, another important change is
that the bin directory is no longer divided into platform
subdirectories (Linux64, Mingw, etc). Executables now go
directly into bin. If you use DEBUGMODE or target 64-bit,
then subdirectories for 'debug' and '64' will be made
though.

Oh by the way, I don't think make clean actually removed
files before on Windows. It should now. I also fixed as
many little inconsistencies like that as I noticed.

And now just an overview of the technical aspects that
shouldn't affect anyone who doesn't REALLY care about the
Makefile...

objs and dep directories have been moved to a make
directory. Makefile.cfg and its variants have been moved
out of their various subdirectories to src/Makefile.d
make distclean removes the bin and make directories
entirely, but make clean and cleandep still only affect
the current build target.

When I say automation, I mean that a lot of copy pasting
in the Makefile has been reduced.

See 7df6a309 and 83a87042. I didn't realize that light
userdata's metatable is shared--like numbers or strings.
So it cannot be paired with a metatable.

I also made a few minor tweaks to Lua cvars, other than
accounting for the double pointer in the userdata.

This reverts commit d4c08a84, reversing
changes made to e100f21d.

Attempt to resolve teleportation resync issue

See merge request !1490

Last-minute fixes

See merge request !1483

This reverts commit c51c4787.

Give TOL_ERZ3 an appropriate identifier (closes #516)

Closes #516

See merge request STJr/SRB2!1471

Let Lua cvars use preset values in addition to MIN and MAX

See merge request STJr/SRB2!1480

Unset zstring if a preset value is used

Closes #487

See merge request STJr/SRB2!1479

This is only applicable for bounded cvars (MIN, MAX),
since otherwise there's no way to allocate a zstring.

Cvars could now have a range (MIN, MAX) plus some preset
values, but Lua could not take advantage of this due to
table order not being guaranteed.

Fix a dedicated crash in Special Stage intermissions (2.2.9 RC1)

See merge request STJr/SRB2!1475

Spritedef add hotfix

See merge request STJr/SRB2!1476

Possible netgame quit crash hotfix

Closes #487

See merge request !1477