- 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.

- (hopefully) a more clear explanation of how --sqdistd-alpha, --sqdist-beta,
  --sqdist-m, and --sqdist-gamma options work;
- actually tested the examples against an updated geomag-algorithms install,
  and it works!

- changed default values for alpha and gamma for command line script
  to zero, which means SV and/or SQ do not evolve over time
- modified SqDist_usage.md to show how to explicitly set alpha and
  gamma to desired values
- MUST modify production scripts to explicitly set alpha and gamma
  before accpeting this pull request.

Made a minor change so that the link in the SqDist.md now points to
SqDistValidate.ipynb instead of SqDist.ipynb. Other very minor edits.

- updated Ipython notebook to used SqDistAlgorithm class and methods
- added unit tests
- added functional tests/demonstrations
- added lots of explanatory Markdown