Switching from RestClient to Faraday

My main motivation is to add support to NTLM for my personal use and #12.
The secondary motivation is that Faraday looks better maintained than RestClient.

Faraday supports multiple adapters:
- Net::HTTP
- Excon
- Typhoeus
- Patron
- EventMachine
- HTTPClient

I plan to use Typhoeus(https://github.com/typhoeus/typhoeus).