xwiishow: toggle key events with 'k' hotkey

Some special devices might not provide the CORE interface so we should
allow running without it. It is still opened by default but we ignore if
it fails. You can now toggle it via 'k'.
Note that the rumble feature might require an active key interface.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
lib: add balance board support

This adds balance-board data reporting support. The kernel provides the
weight data as ABS_HAT?? and we can simply forward it to the user.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
xwiishow: print balance board data

Add a new section which prints balance-board data as four different weight
sensors.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
lib: add motion-plus support

Motion-plus data is reported as a separate hot-pluggable device. Parse
this according to the kernel ABI and provide to users as motion-plus
events.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
xwiishow: show motion-plus data

Print motion-plus rotation gyro data and provide 'm' as toggle hotkey.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
build: include config.h by default

Include "config.h" in all compilations so we don't have to include it
manually. Also make the linker skip all libraries and objects that are not
needed.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
lib: add pro-controller support

Forward pro-controller events to the caller. The Pro-controller is
compatible with the kernel's gamepad protocol so you actually don't need
libxwiimote for it. However, for completeness' sake we include it so
we can easily extend xwiishow.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
lib: add static attributes support

For LED, battery and other sysfs attributes, we need some sysfs helpers
so we can read these 1-line files easily.

This extends the API to support LEDs, battery and static device type
information.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
xwiishow: add support for new interfaces

Add all the new interfaces that were added to libxwiimote recently. We
now print all relevant information.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>