[WIP] Rewriting the Univariate Solver

This PR aims to rewrite a cleaner and robust univariate equation solver.
    - [x] polynomial
    - [x] rational
    - [x] trigonometric
    - [ ] functions solvable by LambertW
Well, we have too many cases of solve's usage in the sympy code, including the sets module.  Someday we will have to covert all this to the new syntax.

> Then there can be cases with infinitely many solutions.

This looks to be a more hard problem.