[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
fixed in https://github.com/hargup/sympy/commit/30799f5dd8f180a66ec8e0764c97fc63224783c1.