[SCHEMA] Use mkdocs-gen-files to generate the glossary

[tsalo]

Closes None, but this should help move us forward on #954.

[tsalo]

Build fails because it's set to strict and there are the following warnings:

[33mWARNING  -  �[0mA relative path to '99-appendices/14-glossary.md' is included in the 'nav' configuration, which is not found in the documentation files
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/09-entities.md' which is not found in the documentation files.
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/09-entities.md' which is not found in the documentation files.
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/09-entities.md' which is not found in the documentation files.
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/03-modality-agnostic-files.md' which is not found in the documentation files.
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/08-coordinate-systems.md' which is not found in the documentation files.
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/08-coordinate-systems.md' which is not found in the documentation files.
�[33mWARNING  -  �[0mDocumentation file '/home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/99-appendices/14-glossary.md' contains a link to 'home/docs/checkouts/readthedocs.org/user_builds/bids-specification/checkouts/1041/src/03-modality-agnostic-files.md' which is not found in the documentation files.

I think all but the first are probably related to #974. I'm not sure how to work around the first one though. I'm guessing that that warning is raised before the glossary file is created.

[tsalo]

I am struggling to get this to work with md-tooltips-link. I'm thinking that the best move is to fork it and change the regular expressions used to specify terms. I'm used to the rst approach, so I'm thinking of trying to support ":term:`Name of Term`" or ":term:`Arbitrary Text <Name of Term>`".

[tsalo]

I'm not sure how to make this work, so I'm going to close it.