ENH: tag glossary

[story645]

Would it be possible to maintain/print a tag glossary, either as a standalone or listing on a the "all tags" page. Enhancementof this would be to be able to filter:

.. tag-glossery: domain

where only tags that contain the word domain would be listed.

This request is sort of a mix of github's labels interface and Matplotlib's math symbol table. The idea is the glossary could pull from some page where the list of tags are defined, possibly a json. csv. py file, or sphinx page.

attn: @esibinga