Add two doxygen cross-references for the logging functions

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
doc: ignore LIBINPUT_ATTRIBUTE_PRINTF in doxygen

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
path: log two errors as application bugs

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
test: fix a path test

Test with the right interface, otherwise checking to make sure we didn't call
open on any device is a bit pointless.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Document the top software button behavior

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>