automate btrfs maintenance tasks on mountpoints or directories

 This is a set of scripts for the btrfs filesystem that automates the
 following maintenance tasks: scrub, balance, trim, and defragment.
 .
 Tasks are enabled, disabled, scheduled, and customised from a single text
 file. The default configuration assumes an installation profile where '/'
 is a btrfs filesystem.
 .
 The default values have been chosen as an even compromise between time to
 complete maintenance, improvement in filesystem performance, and
 minimisation of resources taken from other processes. Please note that I/O
 priority scheduling requires the use of BFQ or CFQ, and not noop, deadline,
 anticipatory, nor the new mq-deadline which uses blk-mq.