Convert XML leadsheets to Impro-Visor playalong files (batch)

Converts xml lead-sheets in a directory to Impro-Visor play-along files in the same directory.

Derived from JazzClub's XML2Impro-Visor plugin:

http://musescore.org/en/project/xml2impro-visor

with a pointer from Jojo-Schmitz to Mark Sabatella's and his batch exporter.

http://musescore.org/en/project/batchexport

It seems to function reasonably, but has had only modest testing so far.