New menu description experiments

[bdarcus]

I guess nobody is really using the forums, but ...

I accidentally pushed a change to the keymaps (was intending to push to a branch), but I think I'll keep it.

Basic idea was to use menu descriptions (rather than command names), and within those to use a prefix to signal context.

I've updated the screenshots on the README.

WDYT?

Minibuffer "reference" context

Buffer "cite" context

[bdarcus]

I've decided which-key just isn't ideal for this, so will de emphasize it.