[beta release] pantsbuild.pants 2.0.0b3

[John Sirois]

The fourth beta for the 2.0.x series is now available on PyPI.

This release brings a few bug fixes and new features. Please refer to the following docs for more details and upgrade notes:

• 2.0 Upgrade guide
• Detailed changelog

Special thanks and welcome to new contributor Cristian Matache!

Thank you as well to all of this release's contributors:
      8 Eric Arellano
      4 Stu Hood
      3 John Sirois
      1 Greg Shuflin
      1 Daniel Wagner-Hall
      1 Cristian Matache
      1 Benjy Weinberger
      1 Asher Foa