Delete multi-spacial M/Z classes.

shapefile_parser/shapefile.py
	-Remove all multi-spacial classes (those that implement
	additional `M` and `Z` measures because they're fundamentally
	identical to the foundation `x, y` classes and are unnecessary
	to implement for a proof-of-concept).
	-Redefine the `PolyLine` class as `Polygon`, because they're
	essentially the same.