benchmark

Print at least three significant digits for times. (#701)

Some benchmarks are particularly sensitive and they run in less than
a nanosecond. In order for the console reporter to provide meaningful
output for such benchmarks it needs to be able to display the times
using more resolution than a single nanosecond.

This patch changes the console reporter to print at least three
significant digits for all results.

Unlike the initial attempt, this patch does not align the decimal point.