gcov: rename 2 options.

gcov: rename 2 options.

gcc/ChangeLog:

	* doc/gcov.texi: Rename 2 options.
	* gcov.c (print_usage): Rename -i,--json-format to
	-j,--json-format and -j,--human-readable to -H,--human-readable.
	(process_args): Fix up parsing.  Document obsolete options and
	how are they changed.

gcc/testsuite/ChangeLog:

	* g++.dg/gcov/loop.C: Use -H option instead of -j option.