Used a simple lookup table for max speed changes, with values that represents a smooth curve

This is a proposal to use a smooth curve for the maximum speed deltas used in the arcade-drive. The values are stored in an array, and thus are a bit easier to see in the code and faster to lookup at runtime. This would likely be overall simpler than a few discrete values, and safer and more consistent than allowing those values to be set via the Smart Dashboard.

We could easily have a single Smart Dashboard "sensitivity" factor that we use to adjust these values or choose between one of 2 or 3 curves. That's a little more complicated, but if we need to dynamcially adjust the max deltas then a single adjustment value would be ideal, especially if the default were relatively stable.

The current commit has only one table (i.e., curve), and the values used are the same as the "smooth" curve in the image. A second table that keeps higher max speed deltas at slower speeds is also shown in the curve, but is not currently implemented in the code.
![screen shot 2014-02-18 at 3 36 51 pm](https://f.cloud.github.com/assets/84732/2200636/d20f3a18-98e4-11e3-9bae-7128001724b4.png)