Issue with prefix handling with term exponents

[stevegeek]

I believe there is an issue with conversions when prefixes are used with exponents.

For example, 3.6 kilo seconds-squared is 1 minute-squared.

> puts Unitwise::Measurement.new(1, "ks").convert_to("s")
1000 s

# but

> puts Unitwise::Measurement.new(1, "ks2").convert_to("s2")
1000000 s2

Should that not be 1000 s2?

eg

https://www.wolframalpha.com/input?i2d=true&i=3.6kPower%5Bs%2C2%5D

But

puts Unitwise::Measurement.new(3.6, "ks2").convert_to("min2")
5066549580791808125/5066549580791808 min2

which is 1000 min2 instead of 1 min2