Extracted respond_with (supports metadata)
Add faraday-middleware

The manual way of parsing JSON for submit actions was not working
properly all the times -- better off using Faraday EncodeJson
Remove useless .register from describe block

It was only there to make specs pass when the solution was to
include RSpec::Core::DSL in the spec
Interpolate route once per respond_with

In a case like:

    delete '/concerts/:id' do
      respond_with :no_content, id: volatile(:id)
      respond_with :not_found, id: unknown(:id)
    end

it's correct to re-interpolate '/concerts/:id' for each `respond_with`
but there is no need to do it if there are extra requests in each case
Bump version to 0.7.0