Added a module for marking methods as deprecated.
Deprecated AWS::Core::Client#http_read_timeout.

The #http_read_timeout is a property of the configuration
and is not consumed by the client.  It should instead
be retrieved from the client configuration is needed.
Example:

    # given
    ec2 = AWS::EC2::Client.new

    # deprecated
    ec2.http_read_timeout

    # prefered
    ec2.config.http_read_timeout
Fixed an issue with AWS::EC2::Subnet#network_acl_association

The #network_acl_association had a bug that caused it to always
return the first association from the vpc the subnet belongs to.
Deprecated methods now only issue a single warning instead of one per call.