one definition of json_object_object_foreach only works on c99 and later

Fix Broken Build, Check ADVANCE_CHAR

We forget to check or use the return value of the ADVANCE_CHAR macro,
and upon compilation an error is thrown because of its lack of use. This
patch checks to see if the macro was successful, and if not replaces the
offending character with a replacement.

While parsing token data, we use the POP_CHAR macro to 'peek' at
character data. This behaviour is noted in the comments for the macro,
yet the definition is left as 'pop'. Changing to PEEK_CHAR does not
imply that the character being observed is removed.

rename AM_CONFIG_HEADER to AC_CONFIG_HEADER

the former has been deprecated and does not work on newer autoconf
versions.

Conflicts:
	json_util.c

json_object_object_length

Fixed test_parse for \f

rename _errno

escape '\f' in json_escape_str

'\f' is a llegal char and should be escape in printbuf

Make maximum recursion depth a runtime option

Some houskeeping