Add speed test

[jessicaaustin]

Add a new test, speed_test, based on "5. Impossible speed test " in the ARGO QC Manual (pg 7).

• name: speed_test
• inputs:
  • time and location (lat and lon) -- similar to location test
  • config: a fail threshold, and/or a suspect threshold
• test:
  • calculate distance from subsequent lat/lon points
  • calculate time difference between two points
  • if distance/time_diff > speed_threshold, then flag the point