dumb implementation of instagram api

update readme of instagram client work in progress

passing instagram client_id

Instagram client uses Oauth2Header and Oauth2Query middlewares

cleanup test
Make Instagram client more complete.

Note that I also removed `user_search` method since I feel it doesn't
really do a lot of things. So probably simply call:

    instagram.get('v1/users/search', :q => 'abc')

would be good enough. However I did add `me` method to get user
information since it's quite common amongst all the API. Note that
we could also get the user info upon calling `authorize!`, but we
still add `me` method for consistency reason.

To try this in console, do:

    i = RC::Instagram.new(:client_id => '...', :client_secret => '...')
    i.authorize_url(:redirect_uri => '...')
    # Copy and paste the URL into browser and authorize, get the code
    # from the URL redirected by Instagram.
    code = '...'
    i.authorize!(:redirect_uri => '...', :code => code)
    # Then you're good to go with the access_token granted by the user.
    i.access_token # => ...
    i.data         # => ...

Hope this is useful!