Add ungrab function.
Small typo libspacemouse.h.
spacemouse.h: move include into ifndef header conditional.
Makefile.in: don't link with absolute path when installing library.
Makefile: add udev as NEEDED during shared object compilation.
spacemouse_device_read_event: by default return error instead of ignore.
spacemouse_moniter_open(): set file descriptor to blocking mode instead of the default nonblocking of udev.