man: add libudev man-pages (skeletons) This adds man-pages for most of the libudev symbols we export. Similar symbols are grouped together in a single man-page, with respective links added. All man-pages contain the full skeleton including NAME, SYNOPSIS, RETURN VALUE and SEE ALSO. However, most of them still lack the DESCRIPTION part. This should be copied from the gtkdoc descriptions in src/libudev/libudev*.[ch]. Any help is welcome! (the whole skeleton is already done, so it's really just about the prose-part of the man-pages to be written). Missing from the man-pages are the following parts: - udev_set_log_fn() - udev_[gs]et_log_priority() - udev_[gs]et_userdata() - udev_list_entry_foreach() - udev_device_get_seqnum() - udev_device_get_usec_since_initialized() - udev_util_encode_string() These are considered legacy, afaik. If not, please feel free to add them now! Furthermore, udev-hwdb and udev-queue are not documented at all (for the same reasons).