Added SOIL sources.

SOIL replaces libpng.
Texture2D now loads using SOIL.
Updated Makefile with .c build rules and SOIL sources.
Removed libpng requirement from README.
Merge branch 'master' into development
Removed Camera from Makefile.
Implemented fullscreen toggling.

Uses 2 GLFWwindows. The fullscreen window is created/destroyed whenever
a switch in to/out of fullscreen is made. The primary window is used as
a resource tank.
Completed merge of changes mostly with texture loading