Does away with /etc/default/mysqld, introduces uci configuration
instead. The init script receives some further brushing up, like a
function (copied from Debian) to get mysqld configuration parameters
easily and quickly.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

Also create a user "mariadb" and use it for running the server. And
add possibility to easily add command line args.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

- create directory /etc/mysql/conf.d as without it the server refuses to
  start
- correct the path to my.cnf in the init script

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

MariaDB is a drop-in replacement for MySQL. This commit adds a current
and stable version of MariaDB to the tree.

Quite a few ideas/patches were copied from Alpine Linux, Busybox Buildroot
and Debian.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>