XML as an input format

There are several points that this PR addresses.

* Lean heavily on the XML parser in the Python stdlib
  * This makes some of the parsing code cleaner and more robust
* Changes to the unit test records to convert from TXT to XML

Things left to do before merging:

- [x] XML as input format for coding
- [x] Data stored within the program as a dictionary
- [x] Flexible and robust output writing
- [ ] StanfordNLP integration
  - This will be pushed to a different PR.
- [x] Dealing with event Issues
  - [x] Coding issues
  - [x] Writing the issues out to a file

As it stands now this PR passes the validation suite and codes the same events from the GigaWord sample as the current master branch.