Use OpenSSL::Digest where possible.

Per #525 it appears that the regular Digest module is not thread-safe. Testing
showed that OpenSSL::Digest on the other hand is working fine.

Currently the SQS related code still uses Digest in one place. I tried
replacing that but this triggered spec failures for unknown reasons. The
OpenSSL::Digest API should be identical to Digest so I'm not really sure what's
going on here.
Route53 health check: ip_address isn't required

http://docs.aws.amazon.com/Route53/latest/APIReference/API_CreateHealthCheck.html#API_CreateHealthCheck_Requests

http://aws.amazon.com/about-aws/whats-new/2014/04/30/route-53-announces-domain-name-based-health-checks/
Adding support to the AWS::Core::Endpoints module for getting hosted zone ids for S3 buckets that are hosting websites.
Added binary and binary set support to DynamoDB batch write abstraction.
Bump version to v1.40.2
Merge pull request #530 from carlhoerberg/patch-1

Route53 health check: ip_address isn't required
introduce custom error for empty multipart upload
Merge pull request #537 from schlubbi/mulitpart_upload_error

introduce custom error for empty multipart upload
Merge pull request #529 from YorickPeterse/master

Use OpenSSL::Digest where possible.
Added a #with_tag method to EC2 collections:

This makes it easier to filter by a paired tag key and value:

   ec2.instances.with_tag('key', 'value')

The #with_tag method provides an alternative the following:

   ec2.instances.filter('tag:key', 'value')
Updated the capabilities banner in the docs.
Bump version to v1.40.3
update sample code to use the default credential provider instead of hardcoded strings in a file
Clarify log_level configuration docs
Fix for Route53::HostedZone#exists?

Route53 rerturns a NoSuchHostedZone error when you attempt
to describe a non-existant hosted zone.  This call was being
used to implement #exists? but it was not rescuing the error.
Updated to the latest CloudFormation API.
Reverts presigned v4 url change to Content-MD5.

Fixes #543
Added support for EC2 CopySnapshot of encrypted volumes.

This adds support for the EC2 2014-05-01 API version.
The `AWS::EC2::Client#copy_snapshot` method will automatically
populated the `:destiation_region` and `:presigned_url` params
for the user to enable copy snapshot on encrypted volumes.
Added support for tags to AWS::ElasticBeanstalk::Client.
Added support to AWS::OpsWork for working with RDS.