Finally wrote tests, found an error.

Tests should cover most of the package. Some need to be refined. Found an error in commands.append where the action guesser was accidentally attempting to modify the master json object. utils.call now returns True if there are no exceptions raised.
Optional conversion for append action (only)

Added an optional conversion action for appending. This is passed as the string mapping in utils.fieldtypes
Somehow the actual changes to commands.append and the corresponding tests snuck out of the commit. git reset is tricky. :/ Also, git should ignore vim swp files now.
Ignore actual json files as well for now.
Modified README
Added convert to float test for commands.append