[Ruby] Add support for Faraday (HTTP lib)

Description

Currently, Ruby API client has a dependency on Typhoeus (HTTP lib).

We want to add support for Faraday to provide more flexibility in choosing what HTTP lib to use in the Ruby API client.

Swagger-Codegen version

Current master (Jul 1, 2016)

Suggest a solution

Similar to Java, we can use the -l/--library option to specify faraday and implement the api_client.rb with faraday so that users can choose which one they want to use.

If anyone from the community wants to contribute on this, please reply to let us know. Thanks