- replace another dict comprehension
 - ensure new style classes are used in Python 2.6
 - change the way the tokens list is used (improves ability to subclass)

 - change way states are used, could give a substantial performance improvement
 - implement a more flexible approach for exchange_file start token search (more extensibile for subclassing)
 - rework/standardise keyword implementation for DATA token

Parser improvements
 - implement error handling for duplicate entity instances
   * parser catches the error, logs it
   * resyncs and continues (the duplicate is ignored)
 - rework the exchange_file structure detection
   * added parser.reset() to allow a more flexible approach to subclassing

(assumes code is under ~/projects/src/stepcode)

…TART tokens

…use string slicing rather than strip()