return 'static' object in _call method

sometimes I want to override __call method for some reason. For example I always want to call say method with language option "'language' => 'ja-jp');".
Initial version of Twilio with App Engine Support.
Use preg_replace_callback rather than the /e option, which is not supported on GAE.
Cleanup the URL fetch HTTP class.
Create a HTTP streams based twilio client.
Create a HTTP streams based twilio client.
Add back the ability to specify a http client as part of the ctor.
Add back the ability to specify a http client as part of the ctor.
Merge remote-tracking branch 'origin/master'

Conflicts:
	Services/Twilio.php