Added an exception class for 429 status code.
Support the signed header.

Now we can enable the signed header by passing client_ips option
to the Instagram.Client constructor.

   client = Instagram.Client(:access_token => "AT", :client_ips => "1.2.3.4")
   client.like_media(123)  # => call API with X-Insta-Forwarded-For signature.

If you do not set the :client_ips option, X-Insta-Forwarded-For is not sent.
Merge branch 'signed-post' of github.com:yssk22/instagram-ruby-gem into yssk22-signed-post

Conflicts:
	lib/faraday/raise_http_exception.rb
Incremented version and resolved merge conflict
Merge branch 'yssk22-signed-post'