pex 2.2.0

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2.2.0

This release adds tools to interact with Pex's new embedded offline
documentation. You can browse those docs with pex --docs or, more
flexibly, with pex3 docs. See pex3 docs --help for all the options
available.

This release also returns to SemVer versioning
practices. Simply, you can expect 3 things from Pex version numbers:

• The first component (the major version) will remain 2 as long as
  possible. Pex tries very hard to never break existing users and to
  allow them to upgrade without fear of breaking. This includes not
  breaking Python compatibility. In Pex 2, Python 2.7 is supported as
  well as Python 3.5+ for both CPython and PyPy. Pex will only continue
  to add support for new CPython and PyPy releases and never remove
  support for already supported Python versions while the major version
  remains 2.
• The second component (the minor version) will be incremented whenever
  a release adds a feature. Since Pex is a command line tool only (not
  a library), this means you can expect a new subcommand, a new option,
  or a new allowable option value was added. Bugs might also have been
  fixed.
• The third component (the patch version) indicates only bugs were
  fixed.

You can expect the minor version to get pretty big going forward!

• Add pex --docs and several pex3 docs options. (#2365)