* Using [`GLib Logging Framework`](https://developer.gnome.org/programming-guidelines/stable/logging.html.en) for logging
* Created new `g_logger` function for logging
* Outputs to `stdout`/`stderr` only when running in `foreground`
* `stderr` for `message`, `warning`, `critical` & `error` levels
* `stdout` for `debug` & `info` levels
* Use `G_MESSAGES_DEBUG=all` environment to enable `debug` to print
* Otherwise, output will be to `syslog` or `systemd journal` (when appropriate)
* Standardized usage of `{LOG_PRIORITY}: ` prefix in log messages
* Only when using `syslog`, otherwise `GLib Logging` will take care of it
* Changed `fprintf(stderr`, `printf` & `perror` calls to `g_logger` calls
* You might want to check them out closely to make sure I chose the right levels
* No changes to `logging/output` were made to "`foreground`" programs (I.E. `render_*`)
* Changed `0`,`1` to `no_argument`,`required_argument` in `getopt_long`'s `long_options`
* Fixed `renderd`'s `foreground` opt (should be `no_argument` [0] rather than `reguired_argument` [1])
* Basic test for `mod_tile` module
* ~~Extended `renderd` log priority onto Mapnik's logger~~
In addition to Render and RenderPrio, add another priority level of RenderLow.
The idea is that if you rerender all tiles by touching planet-import-complete and
thereby likely overloading the server's rendering capacity you want to prioritize rerendering
of tiles that were explicitly marked dirty due to data changes over rerendering
due to planet-import-complete updates.
This is achieved by splitting rendering requests by if they are "old", or "very old".
As the tile expiry sets back the modification date many years, mod_tile splits
rendering requests based on how old the tiles are. If they are no more than a
certain threshold (currently set to one year) old, they are rendered with lower priority.
