Dev: Initial documentation XML files.

I'm going to drive the documentation for the new site from these XML
files, as I believe it will make styling the documentation consistently,
and formatting it specifically for DataTables easier than other options.
For example simply including the related tag, or documenting callbacks.

I think I've got almost everything needed here, although I think I'll
document a few more of the harder methods / options before finally
settling on a format and then blasting through the documentation.