Lkml

- Fix whitespace issue with leading commas (59)
- Enable type-checking for libraries that use lkml (71)
- Include line numbers in syntax tokens and nodes (68)
- Fix parse error for preceding commas in lists (60)

* Fix `sql_preamble` issue (62)

* Allow leading commas in lists (60)
* Handle `dimensions` and `measures` in `query` fields (53, fbertsch)

* 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