Refactored default credentials logic and added an environment credentials provider
Merge pull request #52 from jeremeamia/feature-env-creds

Refactored default credentials and added environment credentials
Adding the ability to disable the backoff plugin
Fixing unit test
Fixing test namespace
Adding performance guide
Making documentation theme more readable
Improved Elastic Transcoder integ tests
Improved Redshift integ tests
More documentation styling fixes
Adding a feedback link to the documentation
Adding tracking code and displaying the correct documentation version
Removing gradient
Linking to the performance guide
Moving SSL information to FAQ
Updated docs to use us-west-2 in samples
Fixing the saved PDF filename
Updated docs related to configuration and credentials
Retrying failed S3 requests where S3 closes the socket with a 400 error.
Closes #29
Cleaning up constructor docblock