Docstrings before beginDocumentation

[mahrud]

People (e.g. #3474) are using somewhat strange techniques to allow documenting methods interspersed in the code.

The benefit of beginDocumentation is that it loads hypertext objects which can be used in document, but technically doc doesn't need any of those. Perhaps we could allow calling doc early and storing the inputs, and once beginDocument is called it should process those early inputs. (Kind of like undocumented' in Core)