Netcode fixes the sequel

See merge request !207

Fix save games for a custom mod not saving to custom home folder

See merge request !209

Made a mistake in the directionchar branch. I'm pushing to master - naughty naughty - but nobody's around to stop me and it's my birthday c:

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.