don't set the boundaries in getBoundary

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
use the received span in start

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
overriding the boundaries is now optional

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
expose new playlist driver methods in generic driver

Signed-off-by: Tomas Neme <lacrymology@gmail.com>
rename boundary to window

Signed-off-by: Tomas Neme <lacrymology@gmail.com>