Add sendmail.rb

sendmail.rb is a simple Ruby script using the SES Gem which allows you to test whether a credential set work before deploying them to your production infrastructure. All options are configured using an environment variable. Especially important for the access and secret keys is to prepend your export command with a space. For instance: " export AWS_ACCESS_KEY_ID=AAAAAA000000BBBBBBCCCCDDD1111".