PROTON-650: Added a help option to proton-dump.

If no arguments are provided on the command line then the help output is
displayed.

Also created a manpage from the help output using help2man.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1618947 13f79535-47bb-0310-9956-ffa450edef68