Sysode linear 1storder 3eq

This PR implements linear system of three equations of first order with coefficients being both constant and function of variable. This PR is also about implementing 'n' homogeneous equations of first order with constant coefficients.
The problem I see with a keyworded argument is that you're basically exposing implementation internals. Basically, you want a static variable. I found a Stack Overflow question that answers this,

http://stackoverflow.com/questions/279561/what-is-the-python-equivalent-of-static-variables-inside-a-function