Now honors proxy environment variables.
Implementing batch message features

new methods in Base.pm to accomodate batch messaging; _get_or_post
(decision to get or post), _escape_param (for escaping MessageBody and
DeleteMessage parameters) and _max_get_msg_size (determine the combine
messsage size)
Implementing receipt verification

new() now accepts the original message body - passed from the
SendMessage method that typically creates the response object. This is
utilised by a new method VerifyReceipt(), which tests that the MD5
checksum in the response matches the md5_hex of the original message
body.
Implementing batch messaging

New methods SendMessageBatch, ReceiveMessageBatch and
DeleteMessageBatch, enabling batch messaging.

For consistency with the new batch method, DeleteMessage now accepts a
message object. For backward compatibility it also still accepts a
receipt handle.

For consistency with other batch methods, included ReceiveMessageBatch
which sets MaxNumberOfMessages => 10. For backward compatibility, can
still pass MaxNumberOfMessages to ReceiveMessage.

Better (and stricter) definition of how returns are dealt with by
ReceiveMessage. Will now return array-ref in scalar context when
multiple messages are expected.

Calls creating new SendResponse objects now pass the message body to
enable receipt verification
dev-methods-batch.t

unit tests for batch methods
perl doc updates

Better documentation in line with the current Amazon documentation
Merge remote-tracking branch 'cjones586/chris-batch-additions'
V2.0 changes, integrate batch patch.