Added ASN.1 utcTime parsing/formatting support

[idyll]

Summary of changes

ASN1 (for crypto) has a specific (kinda ugly) time format - ASN.1 UTCTime.
This PR adds support to parse and format it.

Primarily this is needed to get a DateTime out of a certificate and then use Timex to check how long until that certificate expires. But it's useful for anything that used ASN.1. (Certificates, S/MIME, signed messages.)

Checklist

• New functions have typespecs, changed functions were updated
• Same for documentation, including moduledocs
• Tests were added or updated to cover changes
• Commits were squashed into a single coherent commit

[coveralls]

Coverage increased (+0.08%) to 70.657% when pulling f7131b9 on aai:asn1-utctime into 76b3e11 on bitwalker:master.

[bitwalker]

Looks great! Thanks for the PR, it's much appreciated! I'm holding off on a release until the localization stuff is polished up a bit better, but that won't be long. Hope that's ok!

[idyll]

Thanks! Totally fine. :)