cleanup varlens and make a pip release

[timodonnell]

If we're using this for pgv that's a good impetus to

• write docs
• figure out a way to demote the Python-expression-on-the-commandline stuff to still be there when you need the flexibility but be less in the way in the code
• add unit tests for all the --include-X arguements in varlens-variants
• do a pip release

[hammer]

Done right? https://pypi.python.org/pypi/varlens/

[timodonnell]

Yep.