[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
Addressed in https://github.com/hargup/sympy/commit/bb35d9357db8f8347cdfce0cbd80cbae92ae0a56#diff-d41d8cd98f00b204e9800998ecf8427e