S3 CLI Plugin

This pull requests adds a customized S3 plugin to the AWS CLI.  The purpose of the plugin is to provide better CLI support for AWS Simple Storage Service.  This plugin adds a set of commands that replace the ``s3`` namespace and move the old ``s3`` commands to the ``s3api`` namespace.  The set of commands include:

``cp`` --> Copies a file or S3 object into a location locally or in S3.
``mv`` --> Moves a file or S3 object into a location locally or in S3.
``sync`` --> Synchronizes local directories and S3 objects under a common prefix.
``rm`` --> Deletes an S3 objects.
``ls`` --> Lists S3 objects under a common prefix or all S3 buckets.
``mb`` --> Makes a S3 bucket.
``rb`` --> Remove a S3 bucket.

Note that in order to use the plugin, a region must be specified either in a configuration file or environment variable.

For more information on these commands, use the ``help`` commands.  For example, to get a brief overview of the plugin type the following.
::
    
    aws s3 help

Make sure you read the overview to effectively use the plugin.  The style does differ from the AWS CLI.

For more information about a specific command like ``sync`` type the following
::

    aws s3 sync help

All individual operations are performed in parallel with each other.  This plugin supports multipart operations.  It actually relies on them for files greater 8 MB.   Furthermore, all individual part uploads/downloads of a single multipart operation are performed in parallel as well.