Pull request for Lecture 2 assignments for sea-c28

Fibonacci numbers and Lucas numbers are produced by variations of the same sequence. The only difference is the two starting numbers. If you change those two starting numbers then the sequence should produce a different series numbers. The assignment requests that your sum_series() function be able to accept two starting numbers and return the value of the nth number in that series.

Lots of people weren't sure what to do with this. I'll let Cris know that a more explicit instructions would be helpful.