Add "workq" framework.

This will allow to execute multiple compression/decompression routines at same
time.

Signed-off-by: Adam Tkac <adam.tkac@geodis.cz>
Use workq when decompressing files to allow multiple decompressions at same
time.

Signed-off-by: Adam Tkac <adam.tkac@geodis.cz>
Add support for background compression of files.

Signed-off-by: Adam Tkac <adam.tkac@geodis.cz>