Remove unimplemented parameter w

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Add new function slac_debug

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Add new function slac_debug

Replace all function calls of debug with slac_debug, which is able to
suppress messages

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Disable debug messages in quiet mode (fixes #28)

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>