Preprocess user messages

[helins]

A custom hook on every user message before sending the chat for completion would make this plugin extremely extensible. For instance, a hook might rewrite messages so that a substring like [[file x]] would embed the actual file x. That would open a world of possibilities.

Of course, right know anyone could use some Neovim magic to actually embed the data directly in the chat using commands and such. However, that would often bloat the buffer (e.g. sending a large file) and generally speaking be a limiting factor.

[qaptoR]

I desire this feature as well. I will work on a PR in the coming week or so.

If anyone has an preference or suggestion for what the preprocessor syntax ought to look like, leave them in a comment. There was a plugin for obsidian that had this feature available, and so I will try to make the PR on parity with it.