Dynamically configure template path

[dblock]

I would like to be able to

Grape::Rabl.configure do |config|
  config.tilt_root = -> { "#{env['api.version']}/..." }
end

See #24.

[florrain]

Hey! What's the status of this?

[dblock]

Nobody is working on it, please feel free to submit a PR.

[florrain]

Alright! You have it then. I'll probably propose something here first after looking at the code.

[u2]

But ,this will break our existing app.I just want to use it on specified api.version.