Improved how libraries are specified and found in the CMake files
Reorganized math headers and implemented vec2
Added header files to gfx and gl
Removed unused scalar from vec2
Implemented class quantity for managing scalars of differing units
Clarified template parameter names in quantity
Fixed compilation error relating to incorrectly named template type
Added scalar multiplier free functions for quantity
Upgraded quantity to class and hid value of quantity in private section
Added concept of base_unit to quantity
Cleaned and refactored quantity::per()