Start of Notice/Rule Parsing

This adds a few functions in parser/notice.py for pulling apart the Federal Register xml and converting it into a data structure. The XML doesn't make explicit relationships between various tags, but the generated JSON should rectify that. There are also tests for this.

This adds a script which generates this very simple notice JSON if given an XML file.

This adds requirements files (since lxml is now required), as well as a grammar file, which isn't used yet, but will be for layer generation.