SDL2: Fix 320x200 mode
SDL2: Reimplement some stubbed commands

Also remove some unnecessary functions.
SDL2: Do not use xinput, force directinput

Fixes axes issue with xinput controllers.
SDL2: Add 1600x1200 mode
Initial uncapped framerate implementation
Add cvar capframerate, type CV_OnOff

Default to On
Un-fuck timer code on Windows again
Stub I_GetTimeFrac on other interfaces
Multiply angles directly instead of converting

Fixes the flickery camera issues
Add view contexts

Allows multiple camera renders (2player, skyboxes)
Add common lerp functions

perhaps these can be made inline?
Lerp thing positions
Lerp sector thinkers

Lerping lightlevel and floor/ceiling height for now. Need to lerp flat
offsets at some point too.
Limit water postprocess ripple speed in GL
Uncomment some portal rendering stuff

compiler warnings are scary :(
Lerp T_Scroll-ers
Workaround gcc 4.7 ABI incompat

-mno-ms-bitfields causes 2-byte offset in net packets on mingw builds.
Builds with gcc 4.7+ should now support multiplayer.
Use gcc_struct on ATTRPACK too
uncapped: add cap framerate option in menu