Autobrake & decoupling player sprite angle from camera angle

See merge request !69

Sprite2 MD2s and customisable defaulting

See merge request !115

Save cards and continue startinglives-balancing

See merge request !114

Titlemap

See merge request !97

MI misc whatever

See merge request !111

* Made drawangle updated when jumping off a wall as Knuckles.

* Make rope hangs change how they handle the player's angle a little more organically.

* cv_directionchar and cv_autobrake, and their secondplayer versions (both on by default) now exist.
* cv_useranalog is now hidden from the menu.
* Directionchar now attempts to face the camera direction when you're standing still, and handles a few other states with more decorum.
* Tailsbot is now slightly more capable of keeping up with Sonic.
* pflags rearranged/adjusted, combining a few non-simulstaneous ones and turning PF_NIGHTSFALL into CR_NIGHTSFALL.
* [unrelated to branch] all ground-impact based abilities now happen more consistently with quicksand.

* Clean up spr2 md2 code.
* Experimented but then commented out some stuff for homing attack.

SDL2: Relative mouse mode

See merge request !206

P_FloorzAtPos slope fix

See merge request !208

Don't allow creating a new save when it wouldn't end up making a save file (ie, modified game without savemoddata).

* Fix skidding interpoleration bug.

* Make the model->spr2frames dynamically allocated. (There's only two settings - on and off - but that's better than it perpetually being on...)
* Fix up defaulting for DEAD to go to PAIN.

    - Name each frame either SPR2_**** or SUPER**** (where **** is the 4-character name)
    - If the name is 3 characters, '.' is accepted as a substitute for the '_', but a space/absent isn't (for tool-related reasons).
    - Adds a big sprite2 index array to all models, even non-player ones. Sorry!
* Made MD2 frame interpoleration only work across the same spriteset (and sprite2set).
* Made MD2 frame interpoleration happen when there's less than a quarter of a second between frames, as opposed to the hardcoded specific animation disabling.
* Fixed sprite2-related typo in dehacked.c.

This is in preparation for a seperate project which still involves sprite2s.

Merge branch 'master' of http://git.magicalgirl.moe/STJr/SRB2Internal.git into continue_startinglives

* Added length cap to savegame's zone name.
* Refactor to level select's zone name length cap code.

* Made botskin being invalid make the entire save invalid.

* Update/improve ultimate mode interaction experience a little. https://cdn.discordapp.com/attachments/293238104096112641/349685399200727041/srb20027.png

Also, don't post an ev_mouse event_t if not in relative mouse mode, so the camera doesn't jerk when the mouse enters the window

* Fix an issue where valid savefiles would be hidden because there were at least three unused slots between that and the last visible save. In the process, made sure there were at least three slots visible at all times, but never show extras not needed to show all the saves.
* Optimisations in a bunch of places, including to static
* Fix some visual errors with text and patches near the edges of the screen in non-standard resolutions.

Also did some cleanup and moving around, as well as adding comments

* Add new graphics for the no save and ultimate slots, and make the invalid files look a little different.
* Push big endsign images downwards.
* Add a way to disable the ultimate slot.
* BwehHehHe()

* Changed the save format a little more, since I had free reign over it.
* Modified the string drawing functions to not awkwardly clip at the very edges of the screen, considering the relevant patch drawing functions avoid out-of-range memory writes.

* Per Mystic's request, only set the number of lives in the save file if you actually use a continue, or completely wipe out your lives and continues.
* Fix a bug where I got emeralds and mapnumbers mixed up when checking for the "there's a tailsbot" flag.
* Consider a save with an invalid skin an invalid save, rather than allowing its continued presence.

Turns out the issue was with fullscreen! All I have to do is factor in the resolution/real window size ratio apparently (which was already done before)

Also changed movemousex/y to INT32

This fixes SDL2_RelMouse's weaker sensitivity for me on Windows (but apparently not for others??)

Anyone know if "connect any" work at all? Would have disabled that too but apparently the game uses it if "-connect" is given with no params