Update documentation

[Turnerj]

The current documentation does not cover the changes in the major overhaul commit, namely entity mutation and entity tracking.

[Turnerj]

As an extension to this, better inline documentation should be added to the various core classes and interfaces as well.

Need to setup GitHub pages branch and relevant domain name too.

[Turnerj]

While documentation can never really be "done" while new features etc are added, major documentation improvements were done in bef2985.