Make subjects unique
The subject is made unique by attaching the commit 
SHA hash to the subject line. This (hopefully) prevents 
email clients from grouping code review emails.
Add information about repo and branch as well as commit id to subject line.
Set reply_to email header to be commit author.
Facilitate for configuring the from header.
You can (and must) specify the from header in the email 
by setting the environment variable "SENDER".
Nitpicking
Make example screenshot reflect new subject line.
Nitpicking