Added DescribeDBParameterGroups and DeleteDBParameterGroup RDS APIs
Added ModifyDBParameterGroup RDS API support
Added DescribeDBParameters RDS API support
Added support for the optional Source parameter for the DescribeDBParameters RDS API
Fixed incorrect XML path to the DBParameterGroupName which was causing instances to get recreated
Fixed bug with describing DB instances that use VPC security groups
Added missing test assertion for pulling out the DBParameterGroupName during a db instance describe
Merge pull request #128 from rcostanzo/master

Added DescribeDBParameterGroups, DeleteDBParameterGroup, ModifyDBParameterGroup, and DescribeDBParameters RDS APIs