Lkml

* Add ``BasicTransformer`` class that makes modifying the parse tree easier (44)

* Handle leading and trailing whitespace regression (45)
* Ensure double quotes in quoted fields are escaped (46)

* Completely rebuilt parsing to work off of a concrete syntax tree (parse tree)
* Parse tree now maintains comments and whitespace
* Supports updated filters syntax with key/value pairs
* Integrated GitHub-scraped LookML into tests
* Added Sphinx documentation and published to Read the Docs
* Migrated tests from docker-compose to tox

- Fixed an issue with `bind_filters` plural keys (30)

- Fixed an issue with `sql_where` plural keys (25)
- Added support for LookML data tests (28)

- LookML serialization (generation) from Python objects (14)
- Load LookML from string as well as from a file object (17)
- Added local test suite via Docker (jamescurtin)
- Added docstrings and examples throughout codebase (16, jamescurtin)
- README updates on LookML representation
- Add `CONTRIBUTING.md` guidelines including details on running test suite