Improve searching by showing possible selections from those available in the library as each letter is selected.

So e.g.
Search > Artists >
... choose letter; click
... (next-selection shows all letters, briefly, while json call)
... (next-selection shows only letters which have a match, and if there's only one match show the full name of the artist)

See thread for discussion and background:- http://forums.slimdevices.com/showthread.php?t=41816&page=2