add --without-non-free build option to disable non-free minifiers

Douglas Crockford code is non-free (per FSF definition) as liberty #0 is not granted (restriction).

This is a blocker to include this framework in any downstream distributions which strictly respect the free License (Fedora, Debian, ...). See: https://fedoraproject.org/wiki/Licensing:Main?rd=Licensing#SoftwareLicenses  (search for JSON.org)

So this patch, which is noop with standard build, allow to build using --without-non-free option and disable those filters.