MATH: no need do cast anymore in Matrix4::inverse
MYST3: Fix room background scripts not being run
MYST3: Implement two counter variables and add info about missing variables
MYST3: Remove information about variables never used by the game scripts
MYST3: Implement an hotspot related variable

Fixes the wall symbols subtitles in Narayan
SDL: screen HW surface was never needed. it's disabled/ignored in some SDL ports: win/x11 and osx is emulated with very specific conditions
SDL: make proper use of bytes per pixels in GFX operations
SDL: un-hardcode some GL operations
MYST3: Mark a variable as implemented
MYST3: Add some sound related plumbering
MYST3: Respect the mouse speed set in the settings screen
TINYGL: cleanup types
TINYGL: formatting
TINYGL: use own type
GRAPHICS: Minor cleanup in the Shader class
MYST3: Add yet another sound opcode
MYST3: Remove useless todos