Base64 encode attachments
Set attachment filename independently of on-disk filename
Forgot to import base64 module
Merge pull request #51 from jamiebegin/develop

Work on #37.  Bundles additional feature to re-name on-disk attachments.
Changed excessively large variable argument name.
Base64-encode attachments and wrap to 76 characters.
Version bump.
Merge remote-tracking branch 'upstream/develop' into develop