BigFracPwr class does not support root simplification and rationalization

[mcreng]

Root simplification

Example: (1/4) ^ (1/2) should simplify to (1/2).

Rationalization

Example: (1/2) ^ (1/2) should rationalize to sqrt(2) / 2.
It is proven that only for square roots and those in form of 1 / n^(p/q) where n, p & q are integers need to be concerned for rationalization.