Add documentation for the class fields

[Ghostkeeper]

This adds some basic documentation for the fields of each class provided by this library. The documentation has been reverse-engineered from experimentation and by reading the source code of the library.

I have been frustrated by the lack of documentation in this library, so I've dedicated the better part an afternoon to documenting this. I hope it will be useful to future users of the library.

Since there was no documentation for any fields at all, I've adapted the documentation style of the methods that were documented. The existing documentation was inconsistent in use of periods at the end so I've opted to just use periods there. Some fields appeared to be dysfunctional, so I've skipped documenting those.

Fixes #62

[irmen]

Thanks for taking the time to write this out.

However, what you seem to not have realized, is that the README.md documentation is automatically generated from the python source code (via "make docs").
So the description of these fields have to be inside actual source code.

I will add a note in the readme that the api docs are auto-generated and should not be edited in the readme file itself.

[Ghostkeeper]

I see it now in the setup script.

Then considering these fields are implemented with self.xyz = abc lines in the __init__, how would you propose that this documentation best gets implemented? As far as I know, such python attributes cannot have any __doc__ field. You couldn't really get this from introspection as it is done currently. Like, we'd have to implement some sort of Python source code parsing? AST stuff?

[irmen]

Maybe just add to the docstring of the class itself. But I haven't thought this through very much and I don't really know how the resulting .md file will look like.