THIS IS A BREAKING CHANGE
Switch flags implementation to use pflag. This means that long flags
like `-username` must now use 2 dashes: `--username`.
The `-v` flag (verbose) used to accept `-v` or `--v`. Now it only
accepts `-v.
The `--help` and `-h` flags are new.
The `--man` flag is new (print a man-page like help message).
Several glog flags which used to be exposed (e.g. --logtostderr) are no
longer exposed. Logs always go to stderr.
Tim Hockin