Prepare for 0.0.23 release.

Testing Done:
None

Bugs closed: 469

Reviewed at https://rbcommons.com/s/twitter/r/862/
Add AaptBuild task

AaptBuild constructs the apk out of the dex file and
the targets resource dir. Refactored the Aapt pipeline,
there is now an AaptTask base class. When calling
"bundle" on Android code you should now get an
unsigned .apk as output.

This also adds an AndroidIntegrationTest base class to
simplify Android integration testing.

I moved the 'package_path' method out of codegen and into
the AaptTask because all the aapt methods needed it. If
someone thinks it is truly useful to other codegen methods
I am open to moving it higher.

Testing Done:
CI.sh passes
Travis is failing elsewhere, so no Travis info.
Unsigned apks are indeed generated :)

Reviewed at https://rbcommons.com/s/twitter/r/859/
don't hide docs for exclusives= target param in an unpublished docstring.

A blurb about how to use exclusives was hiding in the CheckExclusives goal doc. Many BUILD dictionary entries mentioned this, but weren't high-tech enough to "hyperlink" that doc.

So... move the "user-facing" exclusives doc out of tasks/check_exclusives.py into docs/build_files.rst.

in many backend/.../targets/*.py files, link to the new location.

Testing Done:
generated doc set, eyeballed

to make sure my automated comment-fixup doesn't destroy the world's syntax, kicked off https://travis-ci.org/pantsbuild/pants/builds/32287735

Bugs closed: 451

Reviewed at https://rbcommons.com/s/twitter/r/865/
Split AddressMapper out of BuildFileParser