Create fast_exponentiation.py

Fast exponentiation. 
This is a fast way to raise a number to an integer power. It requires the fewest multiplies, and does not use logarithms.

Fast Exponentiation of integers, raises n to the p power

Base Case. If  : return 1.0.

Odd. If p is odd: return .

Even. If p is even:

compute ;

return  .

Note: Question taken from http://www.itmaybeahack.com/book/python-2.6/html/p01/p01c09_functions.html