Issue #39

Tests cover:

• a variety of possible combinations of generalized statements as quoted triples
• test position of quoted triples and their nesting up to 6 levels
• checks assertion vs quotation of the same statements
• verifies repeated terms behaviour by placing the same s/p/o in different contexts
• checks lookup tables usage

As the combination of all possible terms/positions in generalized RDF-star is too big, the following combinations were put into the tests:

| S    | P    | O    |
|:-----|:-----|:-----|
| TT   | IRI  | IRI  |
| TT   | BN   | BN   |
| TT   | L    | L    |
| IRI  | TT   | IRI  |
| BN   | TT   | BN   |
| L    | TT   | L    |
| IRI  | IRI  | TT   |
| BN   | BN   | TT   |
| L    | L    | TT   |
| TT   | TT   | Any  |
| TT   | Any  | TT   |
| Any  | TT   | TT   |
| TT   | TT   | TT   |

TT -- triple term, L - literal (one of plain/typed/with langtag)