Changes this commit:
- Merged _Exo_Helpers and _Exo_Php_Helpers
- Changed helpers to support static methods in helper classes in general but still instance methods from Exo_Implementation and Exo_Autoloader.
- Added PhpDoc comments for methods in Exo_Implementation and Exo_Autoloader to Exo_Main_Base.
- Added $dir as required parameter for Exo_Implementation::__construct().
- Renamed Exo_Implementation_Base to Exo_Implementation and moved into /core/ directory
- Simplified Exo class and thus what's required to implement an Exo component/site.