A first version of the `anx-delta-buffers-command' is working.

Given two buffers with wiki tables, one from an existing page, and
another just generated by `anx-really-print-meta', finds all of the
fields just discovered that are not currently documented. Then, it
prints an alist of these fields and how many times they occur in a new
buffer.
Renamed our hashes and some of the functions that work on them more nicely.
Wrote convenience functions for hash building, renamed functions for brevity.

Removed the per-buffer interactive functions for building up old
and new field hashes.
Added docstrings to the delta-generating functions.