Variables, metadata, and hot-keys

[DarkTyger]

Pandoc can read metadata from each document's header. This is a little short-sighted because books can be composed of multiple chapters across separate files --- at least, users shouldn't be penalized for wanting to separate their content into multiple files. This implies that metadata should be externalized.

Once we latch onto the idea of externalized metadata, we can see that metadata is just a fancy name for variables.

It would be great to have variables defined in a file and be able to reference them throughout the documentation. The format for the variables shouldn't matter -- TOML, YAML, XML, JSON, etc. We only need simple string definitions in a hierarchy for organization (so CSV wouldn't be super useful).

Once variables are associated with a document, we need to easily insert variables while editing.

Allow associating a hot-key (e.g., Ctrl+Space) that, when pressed, looks for the word under the cursor inside the variables document. If a substring match is found, the editor automatically inserts the variable reference into the document. A common format for variables is moustache style ({{variable.reference}}), using dots to separate the hierarchy. Note that if the document has dynamic content, then the sigils used to bracket the variable will need to change. For example, R uses backticks while Python may require a different syntax.

This implies that there should be a way to map accelerated keyboard commands into actions. In general, it should be possible to map any keyboard command into any type of action, like a macro. This would allow users to customize stenotype-like behaviours (Chording, Syllabic Input, Briefs and Phrases) with inserting words, phrases, or variables.