This updates constitutes a major re-write of the library.

- Creation of "Collection" concept within the library
- Collections have replaced the need for the ComplexOutput class
- Collections are injected into the base AssetManager class on construct and contain all of the assets available per asset type

- Creation of CombinedAsset concept
- CombinedAssets are similar to Assets except with altered functionality and are only used internally during output.

- Added getters and setters for each config parameter
- Config setters now update a static $portable_config; array.
- Configuration is now available via the public static method \AssetManager::get_config();

Still to do:
- Less support
- Update README.MD
- Additional testing
- Properly implement output_scripts, output_styles, and output_less methods on \AssetManager