Adds acm middleware

hmiddleware: add acm (#73)

This middleware is useful for implementing the heroku ACM specific
contract for redirecting to the origin ACM servers.

Customers shouldn't need to use this if they're just leveraging the
platform normally -- but is more for fringe cases.

testenv: Saner defaults

Allows saner defaults for testenv Redis and postgres, favorable for local development.

more libraries added

• sharder
• logplex/encoding
• hmiddleware/httpmetrics
• basicauth

And much more!

Initial release: go.mod and all the goodness

Merge pull request #60 from heroku/cd-mod-grpc-gateway-bump

bump grpc-gateway version