Add AWS EC2 elastic IP module

Adds a new AWS EC2 module to associate/disassociate instances and
elastic IP addresses.
Fix typo: alises -> aliases
AWS elastic IP: Support for allocating IPs

This commit adds support for allocating new elastic IPs with the
ec2_eip module.
Merge branch 'ec2_eip' of https://github.com/lorin/ansible into lorin-ec2_eip
Minor pep8 cleanup in ec2_eip module