More updates to SqDistAlgorithm documentation

- improved explanation of exponential smoothing, and how the alpha,
  beta, and gamma parameters work in SqDist.md.
- cleaned up command-line examples in SqDist_usage.md, and incorporated
  a description of the programming interface that was previously in the
  IPython/Jupyter notebook.
- removed programming interface description, and cleaned up markdown
  accordingly; re-ran entire notebook and regenerated graphics.