Improve API and expand testing of parse module. Use the new API instead of ParserDB.

### Parse:
* Add `quiet_parse` functionality.

### Parse test:
* Test `quiet_parse`.
* Separate tests of `Parser` class and `parse` module.
* Test `Parser.__init__`.
* Add trivial `pattern` test.
* Use `quiet_parse` instead of `ParserDB`.
* Fix `flake8` warnings. Groom code.

### AST test:
* Use `quiet_parse` instead of `ParserDB`.
* Fix `flake8` warning.

### Type test:
* Use `quiet_parse` instead of `ParserDB`.

### misc:
* Drop `ParserDB`. Fix #65.