Updated docs and version number

I updated the relevant documentation (except for a couple of places
where it looked like the documentation was out-of-date before i got to
it), and bumped the version number to 2.3.1 in various .JSON files.

Note that a bunch of the dev dependencies don't install properly on my
(windows) machine, so I was unable to run the grunt build task - that
still needs to be done before publishing the new version to npm.