Pull cairo overlay stuff out into SDL/i_video

Use platform-specific cairo surfaces

Attempt to resolve font rendering issues on Windows, with little to no
success

Disable status bar caching
Left debugging subpixel hints in by mistake
Fix overlay rendering in OpenGL mode
Update TODO.md, rebuild tags
Add printable character check to HUD input widget

Only allow one foreground widget at a time
Load custom fonts from the "fonts" folder

Remove hacky font loading stuff from hu_stuff

Add some functions to list a folder's files and folders to m_file