bitstring-3.1.7

May 5th 2020: version 3.1.7 released

This is a maintenance release with a few bug fixes plus an experimental
feature to allow bits to be indexed in the opposite direction.

• Fixing del not working correctly when stop value negative (Issue #201)
• Removed deprecated direct import of ABC from collections module (Issue #196)
• Tested and added explicit support for Python 3.7 and 3.8. (Issue #193)
• Fixing a few stale links to documentation. (Issue #194)
• Allowing initialisation with an io.BytesIO object. (Issue #189)