Added support for the CloudWatch Logs service.
Updating the EC2 and Route 53 clients
Added Cognito Identity and Sync clients, tests, and docs.
Merge remote-tracking branch 'cognito' into release-2-6-11
Merge remote-tracking branch 'cloudwatchlogs' into release-2-6-11

Conflicts:
	docs/index.rst
	phpunit.xml.dist
	src/Aws/Common/Resources/aws-config.php
More reliance on environment variables for integ testing

Making it so that the integ tests run without any need to edit config files
if the proper environment variable credentials or ini file is present.
Removing keys from the test_services.json file to discourage placing
keys in this file.
Addressing the double encoding issue in SigV4.

Adding override for S3 as it is not affected.
Adding test for S3 sigv4.
Updating compliance tests to match reality and strip trailing newlines.
Removing the need to have a test_services.json file.
Updating the cognito-identity model
Renaming service access name to match the endpoint prefix
Adding a Cognito alias to the service builder
Ignoring the vendor folder when building the docs
Updating changelog
Allowing APC install to fail and removing 5.6 from allow_failures