Merge branch 'tt/bisect-in-c'

More code in "git bisect" has been rewritten in C. * tt/bisect-in-c: bisect--helper: `bisect_start` shell function partially in C bisect--helper: `get_terms` & `bisect_terms` shell function in C bisect--helper: `bisect_next_check` shell function in C bisect--helper: `check_and_set_terms` shell function in C wrapper: move is_empty_file() and rename it as is_empty_or_missing_file() bisect--helper: `bisect_write` shell function in C bisect--helper: `bisect_reset` shell function in C