Merge pull request #61 from SimonStreicher/master

Calculation of P, N and M matrices for SISO
Included scaled singular value calculation
Refactor to remove duplicated code
Merge branch 'master' of https://github.com/alchemyst/Skogestad-Python
Created a method called zero

Zero calculates the zeros of a state space transfer function using the
modified eigenvalue method. Use my other methods to get the directions
etc...
Merge pull request #63 from stelmo/master

Fixed the "sigh" commit error...
Added State Space zero function
Merge pull request #5 from alchemyst/master

Updating