doc: massive refactor and simplification to migrate to mkdocs

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/keventd.md

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+keventd
+=======
+
+The kernel event daemon bundled with Finit is a simple uevent monitor
+for `/sys/class/power_supply`.  It provides the `sys/pwr/ac` condition,
+which can be useful to prevent power hungry services like anacron to run
+when a laptop is only running on battery, for instance.
+
+Since keventd is not an integral part of Finit yet it is not enabled by
+default.  Enable it using `./configure --with-keventd`.  The bundled
+`contrib/` build scripts for Debian, Alpine, and Void have this enabled.
+
+This daemon is planned to be extended with monitoring of other uevents,
+patches and ideas are welcome in the issue tracker.