feature enables representation of cross, circular and etc.object references in json. initial drafts. thanks for idea to @RealAntithesis. affects #18

A<->B reference would look like:    { kB: {kA: {__path: ''} }
A->B<->C:    {kB: {kC {kB: {__path: '.kB'} } } }
update json_deserializer
implement references in json
Merge branch 'feature/cross-refs-in-json' into develop