Feature/integrate extension point

Added support for custom metadata.

This pull request allows developers to override the Injector and override **processCustomInjectionPoints**.

**RTTI.build()** has been updated to allow specification of which metadata tags should be processed.
e.g. 
    --macro RTTI.build(['inject','post','myCustomMetaTag'])

Added ExtendedInjectorTest to validate that **processCustomInjectionPoints** is called with the expected arguments when custom metadata tags are encountered while the injector processes an injectee.