Reworded the documentation of bool Game::gameStateChanged_ because I am a complete nerd.
Renamed the `vec` class to `vector`. The file has also been renamed (vec.hpp -> vector.hpp).
Put our kickass vector class into a new math namespace.
Fixed some documentation in render_text.h.

The documentation for the one parameter of the invertPalette function was written with a capital letter, which caused doxygen to warn of an undocumented parameter.
By changed it from 'Surface' to 'surface'. I fixed that.