MySQL Option/Variable changes in the docs

In amongst the other changes I made last week to provide the Reverse Changelog, I’ve also added some additional output to the Options/Variable chapter. Basically, for the OptVars Dynamic Docs, we track when each option/variable had a change, either in the value or when it was introduced, deprecated, etc. We can now output those changes for a given version, either an individual one (for example 5.1.30) or toplevel (5.1). The new changes are documented here:

As always, comments, suggestions welcome.