Pytype

* Make typing.NamedTuple a class for Python 3.6+.

* Add --exclude flag to support excluding files or directories from analysis.

* Improve type checking of typing.Generator.
* Enable logging from C++ in debug builds.
* Expose pytype-single's return code.
* Add the ability to record trace data during bytecode execution.

* Tweak the installation instructions and add a quickstart guide.

* Document pytype's platform support.

* Officially support running under Python 3.5 and 3.6.
* Expose pytype-single's --version option.
* Optimization: skip argument parameter combinations we've already seen.
* Bring back pytype-single's --timeout option.
* Add --return-success to pytype-single to report errors but return success.