first try of manipulating registers directly instead of the file interface. completely untested.
clarified a comment
removed file_descriptors definition and UNUSED constant
added -1-entries to the pin_ids array, so get_id returns the right value
gpio_deinit now calls gpio_unexport for every pin before munmap
added a missing comma
Merge branch 'register-manipulation'

I think everybody is using the register manipulation, so I moved the file interface into a special branch