Time - documentation

- Updating documentation for clarity, esp. wrt the now / elapsed /
  physicsTime.

- Marked elapsedMS as deprecated as it is just elapsed based on Date.now
  instead of the high-res timer; both provide roughly equivalent behavior,
  with elapsedMS just falling back to worse-case behavior.
Sprite/Time - lifespan based on physicsTime

- Lifespan is updated based on physics time which makes this consistent
  with fixed-step updates and tweens, etc.
Merge commit '0d9678e512f9037b686ca480907c90f82d5b631e' into wip-time-clarify
Game/Time - updateNumber and updatesThsiFrame

- Changed `count` from 0d9678e512f9037b686ca480907c90f82d5b631e to
  `updateNumber` and expanded documentation; also moved primary usage back
  to local variable.

- Added `updatesThisFrame` which allows (logic) code to detect if it is
  the last update, or if there are pending updates the same frame. While
  it could be adventageous in certain cases it will be problematic if such
  update logic relies in the supplied delta time, as such should change if
  fixed-timing is deviated from or extended updates are done.

- Formatting and documentation.
Time - documentation

- Removed previous elapsed/elapsedMS deprecation as they act differently
  when the game has been resumed, assuming that it has been properly
  paused.

- Refined documentation

- Moved a few properties for better logical grouping

- Annotated timeToCall and timeExpected as protected
Merge pull request #1363 from pnstickne/wip-time-clarify

Time - clarify, Game update expose, and Sprite lifespan update