Darglint

Added
- Added `DAR104` which checks for the presence of types in the docstring.

Fixed

- Updated the flake8 entry point to reflect the new error codes.

Changed

- Updated readme and error description list.
- Move debug- or test-only functions to utils file. Probably this
won't help much with load times or memory use, but it will at least
reduce the risk of parse errors from that code.
- Removed the *google_types.py* target, since that is not used directly
by any source code. (*google_types.bnf* is imported by other BNF files,
only.)

Fixed

- Fixed mypy errors in darglint.

Changed

- Changed the error code prefixes from "I" and "S" to "DAR". This
will prevent collisions with other utilities reported through flake8.
See Issue 40.

Fixed

- UTF-8 encoded source files were not working previously. Rather than
reading the string (and forcing an encoding on the data), we're now
reading bytes and passing that along to the `ast` module. See Issue 46.

Changed

- Changed the long description format to text/markdown.

Added

- A *bin/* folder to hold various development utilities for darglint.
Currently, it holds `bnf_to_cnf` (a utility to convert BNF grammars to
CNF grammars), and `doc_extract` (a utility to extract docstrings from
repositories, and annotate them for use in integration tests.)

- A (crappy) integration test framework. Test fixtures are ignored in git,
since the integration tests are only relevant for local development (and
even then, mostly just release). The integration tests are as follows:

- *goldens.py*: Tests against goldens for individual docstrings. This
attempts to ensure that parsed docstrings always contain the expected
sections after development. Goldens are generated using the `doc_extract`
utility in the *bin/* folder.

- *grammar_size.py*: Tests that the grammar size doesn't increase
significantly. Larger grammars will result in longer parse times, and it
could be relatively easy to accidentally introduce a much larger grammar.

- *performance.py*: Tests performance of the parser against individual
docstrings to make sure we don't introduce a performance regression. Also
tests performance for individual files in some repositories.

- TODO: We still need to add some tests against multiple configurations,
and against entire repositories.

Changed

- Changed the recursive descent parser to a CYK parser. This was a significant
change. It makes darglint much more flexible and extensible. However, it
also introduces a significant performance regression. For that reason, this
will be released first as an alpha, while I figure out how to handle the
performance regression (or I determine whether or not it's even all that
important of a problem.)

Fixed

- Incorrect configuration for flake8. See Issue 35.

- Incorrect check for strictness options *long* and *full*. See Issue 37.

Thanks to sobolevn for these fixes!