Moved LOAD64 macro from l2c_imports.hpp to useful.h
Moved round_to and the various linear interpolation functions from useful.h to useful_visual.h
More formatting fixes
useful.h -> color_lerp():
- added documentation in comments
- changed default value for gamma from 2.2 to 2.0
hitbox_visualizer.hpp -> ATTACK_replace():
- slightly modified formula for changing effect color based on damage