0.8.1

Fixes

• clean command now works properly.
• If bender can't create a container, a useful error message is now being
  printed.

Features

• Warn when you request a change to UID while running in rootless mode (user
  namespaces are tricky).
• If an image build failed, bender tagged the image with a -failed suffix so
  it could be inspected further. Now bender also prepends timestamp so one
  image is not being overwritten over and over.

Minor

• Improvements to documentation in README and --help output.