allowing users to specify EC2_ACCESS_KEY and EC2_SECRET_KEY in their AppScalefile
making sure to pass in env vars when we do appscale destroy, since boto will need them there as well
renamed README to README.md
Merge pull request #209 from nlake44/readme-fix

renamed README to README.md
also setting EC2_URL in environment if we see it
Merge pull request #207 from shatterednirvana/ec2-vars-from-appscalefile

Allowing users to specify EC2_ACCESS_KEY, EC2_SECRET_KEY, EC2_URL in their AppScalefile