[#665] Implement ANDNOT operator in Pattern Matching query engine

[andre-senna]

Resolves #665

After this PR, ANDNOT can be used as a token in PM queries or andnot in MeTTa queries.
ANDNOT is like an AND but its last clause is taken as if it has a logical NOT before it. So, e.g., in this query:

        "ANDNOT", "2",
            "LINK_TEMPLATE", "Expression", "3",
                "NODE", "Symbol", "Similarity",
                "VARIABLE", "v1", 
                "NODE", "Symbol", "\"human\"",
            "CHAIN", "0", "1", "2",
                "VARIABLE", "v1", 
                "NODE", "Symbol", "\"animal\"",
                "LINK_TEMPLATE", "Expression", "3",
                    "NODE", "Symbol", "Inheritance",
                    "VARIABLE", "vc1",
                    "VARIABLE", "vc2",

Which is equivalent to this MeTTa query:

(andnot (Similarity $v1 \"human\") (chain 0 1 2 $v1 \"animal\" (Inheritance $vc1 $vc2)))

We are searching for entities that are similar to human but which there's not a path between it and animal. In the Animals.metta knowledge base, it means we are looking for ent.

There are more examples in the pattern_matching_query_test.ccfile. See queries q15 and q16.