Merge branch 'release-0.61.0' into develop

* release-0.61.0:
  Bumping version to 0.61.0
  Update elb model to the latest version
Raise exception if partial credentials are found

This was previously raising an unhelpful ``KeyError``.
Now, whenever a cred provider has at least the access key,
it is an error if the corresponding secret key is not also
available via the same provider.  You also get a better
error message now as well::

    Partial credentials found in config-file, missing: aws_secret_access_key
Merge branch 'validate-full-profile' into develop

* validate-full-profile:
  Raise exception if partial credentials are found
Add coveralls support
Only include botocore files
Update readme with coveralls badge
Merge branch 'coveralls' into develop

* coveralls:
  Only include botocore files
  Add coveralls support
Don't create auth class if signature_version is None

No auth class is created if either

1. No signature_version exists
2. The signature_version attr exists, but it is None.
Merge branch 'no-signature-version' into develop

* no-signature-version:
  Don't create auth class if signature_version is None
Update CloudSearchDomain model in the latest version.
Bumping version to 0.62.0
Merge branch 'release-0.62.0'

* release-0.62.0:
  Bumping version to 0.62.0
  Update CloudSearchDomain model in the latest version.
  Don't create auth class if signature_version is None
  Update readme with coveralls badge
  Only include botocore files
  Add coveralls support
  Raise exception if partial credentials are found