Numpy docstrings

[davidthomas5412]

Convert docstrings to numpy docstrings throughout codebase.

https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#class-docstring

[davidthomas5412]

Probably worth keeping a consistent documentation style throughout the main module. Right now there is code from @drphilmarshall around the time of original paper which has one style (lots of commented lines to separate methods etc, a docstring that is not quite numpydocstring style) and code from @sweverett that has a slightly different style (documentation but not quite numpydocstring style). If neither of you have objections I was planning to convert the files with these different styles to the numpydocstring style in a fairly aggressive manner to resolve this issue.

[drphilmarshall]

Do it. Today numpy docstrings, tomorrow Sphinx-generated html displayed on readthedocs to the world.