Suggestion: use thousands of kilometres instead of "megameters" by default

At present:

> 1001 km = 1.001 Mm //megameters

I understand why MathJS evaluates the expression this way, given the standard SI prefix system for metric units.

However, scientists & regular people are much more likely to use thousands of kilometers than megameters. It would be nice if MathJS could make a practical exception from jumping to the next largest SI unit in this case.