In --seq mode, a parse error was reported as "need RS to resync", but
parsing continued in the middle of the broken text, so fragments of it
were reported as more errors or output as values.
Set the parser state to wait for the next RS after resetting the parser,
instead of before, so that the rest of the broken text is skipped as
RFC 7464 recommends.
Printing a string wrote each character with a separate call, one
fwrite() per character, or one jv_string_append_buf() for tojson and
tostring, which made output of string-heavy data slow.
Scan ahead for the next byte that needs escaping and write the run of
bytes before it with a single call, without changing the output.
Printing strings is now significantly faster, most of all for long
strings with few characters to escape, and the same applies to tojson
and tostring. With --ascii-output, text that is almost all non-ASCII is
about the same speed, since nearly every byte is escaped anyway.
Michiel van Slobbe