Create borwein_cubic_alternates.py

Herein is contained two separate implementations of the Borwein cubic theta functions atop mpmath. 

mpmath:
https://code.google.com/p/mpmath/

Borwein cubic theta functions:
http://www.math.illinois.edu/REGS/reports10/Schultz.pdf

the q-Pochhammer symbols implementations were used to make this video:
http://www.youtube.com/watch?v=0bSfuwDAxEQ
demonstrating their identity a(q)³=b(q)³+c(q)³