Improved interfaces for PTS instances
Refactored a bit
Implemented a command-line flag to show built-in PTS instances
Improved instance descriptions
Moved well-known names for each instance into the front of the list
Moved the list of built-in instances from Options.hs into Instances.hs
Made `handlePTS' traverse a list of built-in instances instead of mentioning their names
Renamed flag to enumerate built-in instances
Fixed a misleading description
Phrased more precisely
Merge pull request #37 from plmday/master

Improve instances interface and add command-line flag to show built-in instances (see #32)