Add authorization parameters in if configured

Any kind of configured authorization parameters are not passed to api calls from instantiated client 

Again, just starting a dialog with potential fix. I can add tests if you agree this is the right fix.

``` ruby
# Assuming Conf::Github[:client_id]/Conf::Github[:client_secret] is a valid Github auth pair.
github = Github.new do |config|
  config.client_id     = Conf::Github[:client_id]
  config.client_secret = Conf::Github[:client_secret]
end

# Before patch
github.ratelimit      # => 60

# After Patch
github.ratelimit      # => 5000
```