Error middleware support using rack util's symbols as status

[dhruvCW]

support the ability to use the Rack::Utils's status_code symbols instead of integers.

[dblock]

I don't see why not. Update CHANGELOG and we can merge.

[dblock]

Looking at this more carefully, I saw that we were documenting that you could set status with a code in https://github.com/ruby-grape/grape#http-status-code, and we have specs that show you can do this here.

      it 'can be set with a status code symbol' do
        subject.get '/foo' do
          status :see_other
        end
        get '/foo'
        expect(last_response.status).to eq 303
      end

So why do we need this? Or at least should we be removing the call in https://github.com/ruby-grape/grape/blob/master/lib/grape/dsl/inside_route.rb#L196?

[dhruvCW]

So why do we need this?

The reason is so the status code can be a symbol when using the error middleware to generate an error like so error!(response, :forbidden)

IMO the two use cases don't really converge.

[dblock]

Ok, my only concern was if we call Rack::Utils.status_code twice all the time, but it doesn't look like it. Merged.