Pylinac

This release adds a CBCT module for automatic analysis of DICOM images acquired for a CBCT scan using a Varian machine and CatPhan 504.

A PyPI setup.py bug was not properly installing pylinac nor including demo files.
Both of these have been fixed. Fixes 4

Several small bugs were fixed and small optimizations made.
A few methods were refactored for similarity between modules.