Leo's new find-def & find-var commands

[Edward K. Ream]

Leo now supports find-def and find-var commands.  They find the definitions of classes, defs or vars.

They work as follows:

- Select the word at the cursor, if text is not already selected.
- Save the find settings in effect before the command started.
- find-def sets the search pattern to "class word" or "def word" depending on whether word is capitalized.
- find-var sets the search pattern to "word =".
- Set word-find to True
- Start the search at the root position of the outline.

This will find the first definition of the word.  Thereafter, you can use F3 (find-next) to find additional definitions.

When the search fails, Leo restores the Find settings to what they were previously.

A new setting, @bool find-ignore-duplicates (default False), controls whether any search command ignores duplicate matches.  Ctrl-F restarts searches, clearing a list of vnodes that have already been seen.  Any failed search also clears the list of vnodes.

Obviously, this scheme is a bit naive.  The search patterns could be improved.  However, even this simple scheme is surprisingly useful.  Furthermore, these commands have implications that I'll discuss in another thread.

Edward