Spellcheck VarCon README.
Update help output to include british_z spelling.
Add a function to read the varcon.txt file a cluster at a time.

This function will also extract the headword and SCOWL level from the
cluster comment.
Filter clusters with a SCOWL level > 80 in the VarCon translate script.

Also add an option to specify the level.

This closes pull request #82.
Bump the version number in the VarCon translate script.