add canary fetch logs endpoint
Merge branch 'master' into canary_fetch
Started work on a Logplex HTTP API test suite.
Moving from crypto:md5/1 -> crypto:hash/2

crypto:md5(Data) is getting deprecated in favour of
crypto:hash(md5,Data) in R16B02, and R16B01 will be generating warnings
for it.

This is preemptively future-proofing the code so we can keep using
warning-as-errors settings.
Added some tests for `canary_fetch`. Since logplex
doesn't use standard http to deliver the logs the
body isn't tested in this test. That's something 
I'd need to fix by writing a custom http client.
Merge pull request #47 from heroku/canary_fetch

Merge Canary fetch to v69