Merge pull request pivotal-cf#18 from snordhausen/patch-1

fix link to the demo pipeline

added additional example to show how to send email without a file

Removed dependency on gomail library

ensure that if body is empty pipeline does not fail

fixes breaking change for empty message body - pivotal-cf#14

adding as variable that can be replaced

fix bug in build script

merging changes from develop

fix docker image repository name in readme

adding ~/.ssh directory with empty known_hosts file