Begin work on support for the EC2 API.

Add module structure for the EC2 API following the example set by the existing
modules. Begin work on the core Ec2 support -- configuration, signing, etc --
and the first supported command: DescribeRegions.
Add an Ec2 example program
Ec2 core support code (response parsing, etc.) and DescribeRegions command.

Basic support code for the EC2 API -- errors as exceptions, generic response
parsing, etc. -- and the DescribeRegions command.
Rename example EC2 DescribeRegions program source file
Partial progress toward DescribeInstances
Closer to working DescribeInstances
check if instance metadata available

To speed up credential fetching.
Merge branch 'instance-metadata' into feature-ec2
added instance metadata creds to Ec2
aws 10