RDFLib: use `GrammarDefinition` for all turtle parsers, and extend and evaluate the results of parsing.

[tian3rd]

• [x] First, create a class ExpressionDefinition that extends GrammarDefinition, and its purpose is to include all 50 turtle rules inside as parsers.

• [x] Second, for most common turtle files such as .acl and our .ttl file in PODS repo, create a EvaluatorDefinition class whose main purpose is to attach custom production actions to interpret the outcomes of the parsers. With rdflib classes such as URIRef, Graph, we can save the results in the graph.

[tian3rd]

Current progress:

Have integrated all rules in the ExpressionDefinition class, and tested a few turtle files in parsing (in local main function rather than the test file). Check commit https://github.com/anusii/rdflib/commit/8449c129ded498860bf117b44abeb03bbee99e78 for details.

Next is to evaluate the parsed result and save what we want using rdflib classes.

[tian3rd]

Update:

• Evaluator for parsed result is finished and tested for sample files.
• The rdflib graph can now parse valid turtle files (.ttl, .acl) as long as it has the right grammar, regardless of how it's written.

Has met the closing criteria.