Add support for port forwarding.
Describe new functionality in the README and fix some coding style issues.
Make SSH for forwarded ports write to /dev/null

If ssh inherits stdout from vagrant, then when you pipe vagrants output
to another program ssh will also use that pipe. The receiving program
will hang waiting on ssh to exit. To make reasoning about things easier,
I have ruby start ssh directly instead of via a shell. Then I have
spawn set stdin/stdout to /dev/null.
Merge pull request #139 from sciurus/forwarded-ports

Add support for port forwarding take two