Add hid-decode as tool for general report descriptor debugging

Editing the description to reflect the new tool. This will/should/may eventually replace hid-parse and form a triad of CLI tools with hid-recorder and hid-replay. This tool now takes one of several formats:

hid-decode /sys/class/input/event0/device/device/report_descriptor
hid-decode /dev/hidraw0
hid-decode /dev/input/event0
hid-decode hid-recorder.out

and the output is the same as parse_hid, what you'd expect.

Original motivation: The Wacom guys collect the sysfs report_descriptor, so having something that parses it is nice (though it's stored as .txt as well there).