Use environment variables for travis, remove redundant test gemfiles
Fix signature verification for external messages.

Mail::Body.encoded returns an altered string compared to the original if
the original wasn't created with Mail.
Merge pull request #15 from duckdalbe/fix-signature-verification

Fix signature verification for external messages.
Merge pull request #13 from meineerde/feature/cleanup_travis

Use environment variables for travis, remove redundant test gemfiles
Merge pull request #16 from duckdalbe/master

Pin minitest to v4, and ignore vim+ctags-files.
version 0.1.4
refactor signing, preserve Auto-Submitted header

- we do not use the input message directly for signing but instead start with a
  clean part.
0.1.5
preserve names in address headers
0.1.6
dependencies
preserve References: header
0.1.7
amend readme to also mention planio in credits