Distance formatter

Formats distance to display based on the following criteria:

* Distances over 0.1 miles return distance in miles with a max of one decimal place.
* Distances under 0.1 miles return distance in feet rounded down to the nearest 10.
* Distances under 10 feet return the actual value in feet in normal (list) mode.
* Distances under 10 feet return "now" in real-time (navigation) mode.