rackup-like newman runner

[practicingruby]

There is an ugliness about how default_logger works that makes us jump through a lot of hoops rather than being able to use Newman::Server.simple! here, and that'd explain the ham-fisted server configuration stuff. But otherwise, this implements --tick, --debug, and --config /path/to/config.rb.

@ericgj If the general idea looks sound, let me know. I'll then document it and add some usage instructions to the wiki, then merge it into master. After that, I'll work on cleaning up the default_logger stuff.