Extended repoze.sendmail with `/usr/sbin/sendmail` binary support from http://github.com/jvanasco/pyramid_sendmail
added `-t` flag for sendmail command to parse message headers in all scenarios
fixed docstring
added CHANGES and CONTRIBUTORS as requested
No need for a separate /usr/sbin/sendmail delivery component, just use direct:

Refs #15.
Use subprocess for /usr/sbin/sendmail invocation:

os.popen is quasi-deprecated, also do cleaner argument handling that
doesn't depend on shell parsing and makes the command templating simpler.
Don't invoke /usr/sbin/sendmail when running tests!  Also add actual asserts.

Refs #15.
pep8