Refactor http codebase

This change-set tries to optimise the way the http related code is
organised for better readability and extensibility. It uses
streadway/handy as the JSON based logging middleware and in the same
fashion implements a metrics middleware to expose prometheus based
telemetry.
Merge pull request #6 from soundcloud/http-refactor

Refactor http codebase
Bump version
Fix initialization flag depend objects
Bump version
Migrate to new client_golang.

This should only be merged once the new client_golang in merged into
its master branch.
Remove redundant metrics.
Merge pull request #7 from soundcloud/migration/new-client-golang

Migrate to new client_golang.
Bump version