AES GCM vectors from NIST

* http://csrc.nist.gov/groups/STM/cavp/documents/mac/gcmtestvectors.zip
Merge pull request #179 from reaperhulk/gcm-vectors

AES GCM vectors from NIST
add some error parsing macros
Also linkcheck the docs
Update the requirements file for our direct invocations of coverage
Merge pull request #185 from alex/linkcheck

Also linkcheck the docs
Merge pull request #186 from alex/reqs

Update the requirements file for our direct invocations of coverage
Merge pull request #181 from reaperhulk/error-handling

Add some error parsing macros