added JSON serializer

the JSON serializer is not yet implemented completely
many stubs have yet to be implemented
completed simple JSON implementation

unit tests and verification still nyi
doesn't (de)serialize imports
works on old absy (so no qualified ide support yet)
implemented signature matcher

also added tests for the signature tester (yo dawg!)
Merge remote-tracking branch 'origin/parser' into module_serializer
merged parser and module_serializer branch

moved serializer according to new folder structure
serializer implementation needs to be adapted to new syntax
serializer now works on new syntax

import syntax not yet supported
implemented serialization support for imports

support currently very naive
relies purely on module name as unique identifier
Merge branch 'module_serializer' of github.com:SL2Team/sl2 into prelude
prelude stub compilation results in prelude_stub.js
Merge branch 'prelude' into externdefs