Use relative import to allow vendoring
Require 100% test coverage
Implement PEP 440 versions
Implement PEP 440 specifiers
Create an invoke task to check PEP440 compliance with PyPI
Allow alternative syntax for backwards compatability
Allow identity comparisons, even for non PEP 440 compliant versions
Normalize post releases like pre-releases and development releases
Do not throw away trailing digits for representation

Instead of normalizing 1.0 to 1, we'll continue to keep all of the
digits that a version normally contains so we can more faithfully
recreate it. The compare key will still continue to drop trailing
zeros for comparing versions.
Fix the normalization of letter versions and local versions
Switch from : to ! to denote an Epoch

The : character has special connotations on Windows, which makes it
an invalid character, so we'll use ! instead which is not an invalid
character.
Allow empty specifiers
Implement LegacyVersion which can support arbitrary versions
Rename identity to arbitrary and assure it operates on strings
Refactor normalization to handle LegacyVersion