Documentation

This release is less functional, but extremely practical.

Comprehensive docstrings were added to all classes and methods as a pre-requisite to automatically generate documentation using Sphinx.

The infrastructure was included to generate this documentation, as is available now available on read the docs -- of which the documentation will reflect the latest released version of this repository.

Some other changes were made to the Joint and DOF constructors, but these are minor and are outlined in the documentation ;)

Coverge at 99% -- report attached.
PDF of documentation included.
Coverage report.pdf
skydy-readthedocs-io-en-latest.pdf