2013 survey

  - Calculate medians as well as average salaries.
  - Decline to report results if there are 2 or fewer responses in any category, because e.g. reporting the average results of one respondent is not anonymized.
  - Update specs to use `expect` syntax.
  - More specs.
  - Use a helper class instead of monkey-patching Array.

I have NOT included the actual anonymized survey data in this public repo.  Will contact you privately.