add new command line options to rptrender

This PR adds new command line options to `rptrender`. These allow the program to connect to a Postgres database server through a UNIX socket directory. Extending the existing `-databaseUrl` option seemed like the wrong approach because all of the possibilities led to really weird-looking URLs. In addition, error reporting now goes to stderr if that seems appropriate and there's command line help.

See
- https://github.com/xtuple/xtuple/issues/2024
- https://github.com/xtuple/xtuple-server/issues/212
- https://github.com/xtuple/xtuple-server/issues/223

Before merging: do we want to propagate these command line changes to the rest of OpenRPT's apps?