Add ability to get historical rank data (rank over time) for a user

[nikkelma]

Some rank-based organizations want to make sure certain rank limits are adhered to, and currently only "end of season" ranks are available to be retrieved. Would love to discuss options for retrieving the historical data (rank vs. time) of users.

Options for time frequency could include...

• Fixed time intervals - return rank data with a fixed time resolution.
  • A request for a week of historical rank data would return the same number of data points each time.
• RLS deltas - only return changes in rank stored by the RLS database.
  • A request for a week of historical rank data would return only as many data points as there were changes in rank that week.
• Hybrid - use the RLS delta time frequency to return data points in most cases, but if a player's rank was updated frequently in one period of time, condense these changes into a single data point based on a fixed time interval.
  • A request for a week of historical rank data would return a maximum number of data points based on the fixed time interval, but periods of inactivity could be "compressed" into fewer data points.