Added classes 'Asset' and 'AssetManager' ; Handles the lifetime of objects derived from the class Asset;
Changed classes 'Shader' and 'Texture' are now derived from Asset, to enable their management through the new AssetManager.
Removed some commented bits of code.
Renamed Graphics.h/.cpp to GL.h/.cpp.
Updated Specification.txt.
Renamed header defines, such as: VERTEXBUFFER_H, to VERTEX_BUFFER_H, for better readability.
Renamed Shader function fromFile to fromFiles
Added Shader function fromFile ; Takes the filepath to a special .glsl file, combining both vertex and fragment shader code into a single file.
Removed some unnecessary include statements.