feature request: ligature hotkey

We are thinking about making the connected clivis shape in Hufnagel work similarly to ligatures in square notation (two pitch symbols that end up visually connected in a particular glyph shape). If so, we would want a hotkey, since this symbol crops up pretty frequently in Hufnagel. (But we don't need to wait till we have Hufnagel! it would be perfectly useful and helpful on square notation.)