Feature/epilogue

[jhillyerd]

Rebase & cherry pick of @pedrinimm contributed PR #41 for issue #32:

Epilogues are now used by spammers or attackers to insert malicious content into emails, this content comes in the form of other mime parts, these come right after the closing boundary of an email.

[coveralls]

Coverage decreased (-0.4%) to 85.801% when pulling 12a6e7b on feature/epilogue into bdc4ef5 on develop.

[coveralls]

Coverage decreased (-0.5%) to 85.789% when pulling a408d9d on feature/epilogue into bdc4ef5 on develop.

[coveralls]

Coverage decreased (-0.5%) to 85.777% when pulling 0c0d1bc on feature/epilogue into bdc4ef5 on develop.

[coveralls]

Coverage decreased (-0.5%) to 85.752% when pulling 68e689d on feature/epilogue into bdc4ef5 on develop.

[jhillyerd]

On my dev machine, average benchmark is quite slow:
BenchmarkSplitEpiloge-4 5000 369788 ns/op 195.05 MB/s

For comparison the quoted-printable cleaner gets 94,898,401 MB/s

[coveralls]

Coverage increased (+4.3%) to 90.521% when pulling c5263a1 on feature/epilogue into bdc4ef5 on develop.

[coveralls]

Coverage decreased (-0.08%) to 86.161% when pulling df2387a on feature/epilogue into bdc4ef5 on develop.