This is a major update: I have incremented the version number to 0.9.

1. All shell operations now have their return codes checked and non-zero
   return-codes result in panic. This feature was requested by many
   users.
2. Major updates to textgrid.py (see relevant github repository)
3. Went to `str.format`-style printing
4. Status messages are improved and now printed to stderr
5. The MLF printing status message lists the number of files found.
6. Fixed possible dictionary bug.