fix soy.atoms.Vector math

[ArcRiley]

Vector math is currently wrong.

For example, mul on an real number should perform a scalar operation which increases the length by the given amount, not by multiplying each component by the scalar independently. In the current form, two vectors of same length but different angle, multiplied by the same real number, will result in different lengths.

See http://en.wikipedia.org/wiki/Vector_(spatial)#Scalar_multiplication for more.

[ArcRiley]

This is a good example of why I shouldn't write tickets in the middle of the night.