`libcurl` & `libcairo` are also optional and their usage can now be optionally disabled (along with `libmemcached` & `librados`.)
* No longer test macOS Autotools building
* Add support for reading `renderd.conf` to `render_expired`
* Add support for reading `renderd.conf` to `render_list`
* Add support for reading `renderd.conf` to `render_old`
* Add support for reading `renderd.conf` to `render_speedtest`
* Move renderd/render_* execution tests to own files
* Reduce variable scope & minor clean up
* Use `stat` rather than `access` to check if file exists
And setting it to `0`, no longer requiring defining it everywhere except in foreground executables as needed.
_Also_:
* Require `GLib` >= `v2.50`
* Needed for [g_log_writer_standard_streams](https://docs.gtk.org/glib/func.log_writer_standard_streams.html)
* Set FreeBSD job `BUILD_PARALLEL_LEVEL` & `TEST_PARALLEL_LEVEL` environment variables via `run`
* Rather than hard-coding them