Misc. shader changes.
Changed tags to layers.
Simplified camera setup.
Added window hint setting.
Added File IO utility class.

It can perform simple operations such as:
- Reading text files.
- Moving / copying / deleting files.
Updated example.
Now using new File IO functions.
Texture class improvements.

The texture class no longer stores the raw texture handle.

Instead, it stores a struct of data.

This allows additional data (such as texture dimensions), to be stored.
Beginning of the GUI system.