Mantissa 0.9.0

• Mantissa is now officially supported on PyPy.
• Expired web sessions are now actually cleaned up.
• Certificate creation now uses cryptography.
• SSH key management now uses cryptography instead of PyCrypto.
• The Mantissa SSH server key can now be rotated with the use of the
  axiomatic mantissa ssh keyrotate command; it is strongly recommended to
  do this for any existing Mantissa sites, as key generation previously
  generated 1024-bit RSA keys which are insecure.
• Any domain for which an internal user exists will now be recognized as a
  canonical hostname, allowing for relative/path-absolute URL generation.