Class-based paradigm for pattern construction

[bskinn]

Token, Line, and Pattern objects

+ operator always constructs Line objects. & always constructs Pattern objects. & has lower operator precedence, which should make complex expressions coalesce in a sane way.

__repr__() for each class should be dovetailed with the objects' constructors to allow re-instantiation of the object.

The head, body, and tail of Parser then will really just take Pattern instances (as well as Parser instances), though automatic promotion of Token --> Line --> Pattern would make sense as a helper.