Pytype

* Improve the display of tracebacks in error messages.
* Make several Python 3 fixes and improvements, including better enum support.
* Fix evaluation of conditionals inside closures.
* Improve handling of comparison operators.
* Add a --strict-import option to not load submodules not explicitly imported.

* Generate default type stubs for pip-installed dependencies.
* Remove the output directory at the start of each pytype run.

* Improve Python 3 varargs and kwargs support.
* Support user-defined generic types.
* Improve --generate-config to show a full sample config file.

* Allow the command-line `inputs` option to be specified in a config file.
* Support hidden files.
* Make the behavior of --exclude more intuitive.

* Support setting --exclude in a config file.
* Add support for annotations in inner functions.
* Officially support running under Python 3.7.

* Update typeshed pin to commit c968124 from September 6.