Removal of Python 2 support

Changes for release v2_2. (googleads#177)

* Google ads v2_1 release

* Fix formatting typo in README
* Add AdWords -> Google Ads migration examples

Update signature for customer_service.create_customer_client method t…

…o give

default values to optional parameters.

* Add load_from_dict method to the GoogleAdsClient

* Update add_expanded_text_ads example to add multiple ads
* Add build status badge to README

* Add load_from_dict method to GoogleAdsClient

* Update add_expanded_text_ad example
* Add build status badge to README

Release version 3.0.0

Release 2.4.1

Release 2.4.0

Releasing v2.3.0