Add rspecs

[lacostej]

Look at the Pending tests to implement. Currently

Pending:
  Freshsales::Client making requests GETs hashes with symbolized keys
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:52
  Freshsales::Client making requests GETs hashes with non symbolized keys
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:53
  Freshsales::Client making requests POSTs string body
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:55
  Freshsales::Client making requests POSTs Hash body
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:56
  Freshsales::Client making requests PUTs string body
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:58
  Freshsales::Client making requests PUTs Hash body
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:59
  Freshsales::Client making requests DELETEs
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:61
  Freshsales::Client making requests converts errors
    # Not yet implemented
    # ./spec/freshsales/client_spec.rb:63
  Freshsales::Cursor#each enumerates when no block given
    # Not yet implemented
    # ./spec/freshsales/cursor_spec.rb:27
  Freshsales::Cursor#each enumerates with blocks
    # Not yet implemented
    # ./spec/freshsales/cursor_spec.rb:28
  Freshsales::RequestBuilder pagination enumerates pages with #get_all_pages
    # Not yet implemented
    # ./spec/freshsales/request_builder_spec.rb:40
  Freshsales::RequestBuilder pagination enumerates elements with #get_all
    # Not yet implemented
    # ./spec/freshsales/request_builder_spec.rb:41