Merge branch 'en/xdiff-cleanup-2'

Code clean-up. * en/xdiff-cleanup-2: xdiff: rename rindex -> reference_index xdiff: change rindex from long to size_t in xdfile_t xdiff: make xdfile_t.nreff a size_t instead of long xdiff: make xdfile_t.nrec a size_t instead of long xdiff: split xrecord_t.ha into line_hash and minimal_perfect_hash xdiff: use unambiguous types in xdl_hash_record() xdiff: use size_t for xrecord_t.size xdiff: make xrecord_t.ptr a uint8_t instead of char xdiff: use ptrdiff_t for dstart/dend doc: define unambiguous type mappings across C and Rust