Rework the JSON escaping function.
Rework the JSON escaping function.

Cover all the cases mentioned in RFC4627.

Reviewed-by: Simo Sorce <65f99581a93cf30dafc32b5c178edc6b0294a07f@redhat.com>
Closes #132

frenche/mod_auth_gssapi,frenche/mod_auth_gssapi,frenche/mod_auth_gssapi,frenche/mod_auth_gssapi