Add the type of norm as an input for Power Iteration

[smturro2]

Power iteration has better convergence if you normalize the output vector after every iteration. This can be seen in the current code. In some case it is better to normalize by the infinity-norm than the 2-norm. I will add an extra parameter to the function so the user can change the type of norm used. The default value would be 2, so existing external implementations of the code will not be altered and would not require changes.

I'm excited to contribute!