Walk multipart emails + extract match from regexp

[martinhill]

I needed to retrieve content from multipart emails via IMAP. Imaplibrary could only handle simple emails, so I added a few new keywords. Perhaps others would find these useful..

The only new dependency is the standard email module.

The second commit adds a keyword to extract matches based on a regexp parameter.

Thanks Martin

[memcmp]

merged and released: https://pypi.python.org/pypi/robotframework-imaplibrary/0.1.1