Add body and index to BatchSendError.failures

* Add :message_body and :batch_index to entries in BatchSendError.failures.

* Updates specs to reflect this

Updates specs to reflect the changes.
Update documentation for BatchSendError.

Note that the previous documentation was copied from
BatchChangeVisibilityError and contained inaccuracies.
Add Simple Token Service API support for Govcloud region, which has a different API endpoint
Added support for AssociatePublicIpAddress option in LaunchConfiguration. Fixes Issue #372
Duplicate frozen strings before forcing the encoding to prevent a RuntimeError
Update publish.rb
Expose the create_date attribute of access keys.
Add test of create_date.
Expose upload_date attribute on certificates.
Add test for signing cert upload_date.
Added support for new resource management features in AWS OpsWorks.
Added support for Reserved Instance instance type modifications in Amazon EC2 (API version 2013-10-01).
Bump version to 1.21.0
Merge pull request #377 from Optimiza/patch-1

Update publish.rb just for the usage message
Add conditional to STS to work with both govcloud and commercial API endpoints
Merge pull request #369 from dfried/sts-govcloud

Add Simple Token Service API support for Govcloud region
Fixed an issue with uploading files to Glacier in Ruby 1.8.
Updated the list of supported AWS API versions in the README.
Fixed issue with SimpleDB::ItemCollection#where.

If a placeholder received a substituted value that looked
like another placeholder, then an `ArgumentError` was
raised.

Now placeholders in the final string are checked against the
original to see if they are actual placeholders that were
not replaced before raising.

Fixes #386
Corrected the documentation for AWS::S3::ObjectCollection#create.

Fixes #368