Add glossary/endnote functionality

[binford2k]

This will allow the user to add glossary terms, either inline or in .callout notes. This is intentionally undocumented for now, as it's not considered to be production ready yet.

On a slide, use something like the following to add both an entry in the notes/handouts and to a page tagged with glossary.

[a phrase](glossary://term-with-no-spaces "The definition of the term.")

You can also add a term to the notes/handouts, in which case it will be listed on the glossary page, but not shown on slide:

.callout.glossary By hand, yo!|by-hand: I made this one by hand.

You can also add a term to a named glossary inline:

[a phrase](glossary://name/term-with-no-spaces "The definition of the term.")

Or as a note:

.callout.glossary.name By hand, yo!|by-hand: I made this one by hand.

---

The glossary page is simply tagged with glossary and an optional name.

<!SLIDE glossary>
# General Glossary

You can add any markdown you want up here. A list of glossary items will be added to the end.

A named glossary

<!SLIDE glossary name>
# This is a named glossary

You can add any markdown you want up here. A list of glossary items will be added to the end.

Fixes #227

[binford2k]

When printing to PDF, it looks like both notes and handouts appear. 😢