[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/39f12b9f5c097fe87a5d1f068ded37cc6bbc2ff7.