[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
This was a bug, it has been fixed in https://github.com/hargup/sympy/commit/450ec6e2fa451baefd0dde4a32db8cae0c14d240.