Fix for issue #282

The fix limits recursion depths when parsing arrays and objects.
The limit is configurable via the `JSON_PARSER_MAX_DEPTH` setting
within `jansson_config.h` and is set by default to 2048.

Update the RFC conformance document to note the limit; the RFC
allows limits to be set by the implementation so nothing has
actually changed w.r.t. conformance state.

Reported by Gustavo Grieco.
static void lex_free_string(lex_t *lex)
{
    jsonp_free(lex->value.string.val);
    lex->value.string.val = NULL;
    lex->value.string.len = 0;
}

static void lex_free_string(lex_t *lex)
{
    jsonp_free(lex->value.string.val);
    lex->value.string.val = NULL;
    lex->value.string.len = 0;
}
