Recommended usage: in `~/.owl/startup`, bind a key like

	bindkey edit C-k command replace-digraph

then while text editing, if you want to input a digraph, type two characters
and then hit CTRL+K. (This is the opposite order of how you do digraphs in vim,
where you hit CTRL+K *before* typing the two characters. I'm sorry, it's the
only way to make it work.)

It comes with all RFC1345 digraphs, like vim. You can put extra digraphs in
`~/.owl/digraphs`; for the format and some suggestions, see
`digraphs.example`.