Merge pull request #7 from cmc333333/master

Merge in Grammars, Tree-Parsing, and move code into parsing package
Getting the external parser to work for Public Law citations
Merge branch 'master' of https://github.com/eregs/regulations-parser
Added a TERMS file
layer.py
Making external citations look like layer interface
Refactored the interface for layer generators, making things more consistent
Moved terms.py to a location lower, that makes more sense
Separated the grammar from the parser
Removed the different layer generators, as they are now unecessary
Moved generate_layers to where it can access modules correctly
Fixed syntax error
Made pre_process a pass method in layer base class; most layers don't need this
Table of contents layer is smarter now, refactored tests to use node building code
Merge pull request #13 from khandelwal/master

Refactoring of the Layers Interface
Removing unused libraries
First stab at interpretations layer