add simple scheme define (aliases)

[nittka]

simple scheme defines referrable as assignments, allowing two more integration test cases to pass

I am not sure what name and value may look like, so the SimpleSchemeAssignment rule may still be refined

[nittka]

I used the markup/markuplines pattern for markuplist as well, which seems to fix further test cases. I also analysed errors I got from the snippet repository files. For two of the error classes I added grammar regression tests which do not pass yet.

[thSoft]

100% test success comes closer and closer...