Solving cubic equations

[elcritch]

There also looks to be a wrapper for SymEngine derived from SymPy but in C++. 
Looks like it has a `solve_poly` as well as `diff` and a few others.

<https://github.com/SciNim/symengine.nim>

Example:
    
    
    let x = newSymbol("x") # symbol
    let y = newSymbol("y") # symbol
    let xPlusY = x + y # expression
    echo diff(x^2, x) # first derivative
    
    
    Run