Concurrent Scanners and Parsers

[tdauth]

• Add class Scanner which tokenizes a string or string stream. A token has line and column information.
• A parser uses the scanner to get the tokens and create the AST.
• Scanning can be done concurrently.
• Parsing maybe as well if the type information can be resolved later and missing declarations as well.

[tdauth]

Makes only sense as soon as we support more than one document or maybe importing files.