CSE improvement

[tBuLi]

This PR changes the current sympy based CSE to a direct port of GAmphetamine's CSE. This port is well worth it because this is the only CSE known to produce the hand optimized solutions in known cases in 3DPGA.

Todo:

• Port polynomial.js CSE code
• Update docs
• Maintain the sympy based code printing path as we still need it in Torch compatibility #117 and other places where we want to print non-python code.
• Use the new CSE in the SymPy path.
• Connect the new CSE properly to the existing printing infrastructure.