Remove SDK code
First commit of injection library

This is still a prototype.  Much of the strafing functionalities have been
implemented, though they have not been extensively tested.  We have added
trigger display which can be turned on/off without map restart with
sv_show_trigger.  Rendering is disabled when r_norefresh > 1 is specified,
which can double the frame rate.  A basic custom HUD has also been added.
Remove unnecessary declarations in common.hpp
Updated README with basic instructions
Use -ffast-math for injectlib
Don't run edgefriction check when speed is very small

Previously when the speed is zero, division by zero will occur and the
subsequent FP mess will reduce the frame rate by half.
Implemented tas_cjmp
Update postype after autoactions to make strafing correct
Check oldbuttons to see if jumping is actually possible
Prevent NaN after applying friction when speed is zero
Implemented tas_dtap
Added entity health HUD
Don't jump if IN_JUMP bit is set in oldbuttons
Incorporate basevelocity into playerinfo_t
Refactoring, added gravity calculation, position update
Move changing of postype into do_movements
Implemented tas_jb
Implemented tas_db4c

More testing needed.
Load pfnRegisterVariable from gEngfuncs
Added cl_db4c_ceil