docstring: thrift_library only publishable in alternate universe
doc: base dir docs were "TODO", replace with Wickman wisdom
Fixup __init__.py

I had added a manual namespace package and this no longer
appears necessary and in fact breaks pip installed pants
py & build commands when used to create pexes.
Cleanup pants.ini keys involved in pants bootstrapping.

This is a result of building a clean, minimal chroot to built Twitter in-house pants.
The change removes some now dead keys from commons pants.ini and inserts
defaults for other keys such that no pants.ini contents at all are needed to build
 a pex from a pip installed pants.
Add "pants developer center" documentation section.

Move developer-focused docs into a "Pants Developer Center" subpage. The
sidebar is getting pretty tall, and this stuff has become large enough to have
its own page. No URLs change - links are just consolidated in a subpage.

Also delete the now unneeded migration guide.

Testing Done:
Generated the site locally and things look good.

Reviewed at https://rbcommons.com/s/twitter/r/70/
java pingpong: remove file copies

Twitter-internal, we moved this sample app's code around. Then we merged.
Whoops, the default merge got files in the old and new location. So clean up.
Clean up imports
Fix errors reported when generating the Sphinx site.
create idea of a Package which is an extension of a Link but compatibility-aware.  this simplifies things.
patch up pants to work correctly
Remove outdated migration guide.
stash a hack for the finders...clean up
Fix cross-device renames in PythonInterpreterCache.

Bugs closed: 241

Reviewed at https://rbcommons.com/s/twitter/r/81/
Merge branch 'master' into wickman/pep425
complete wheel support