Use POSIX getop processing

No new functionality, but command line syntax has changed.
  - git and help are no longer interpreted as arguments
    Use '--git', '-g', '--help', or '-h'.
  - The port number is now specified using '--port' or '-p'.
Backward compatible CLI options
Added options to set listen address
Describe new syntax and features in Readme.md
Changed Readme.md format to look better on GitHub
Merge pull request #6 from jdunmire/master

Set listen address