[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/e58ac5ad9fe81be73e3069edff07f49b7805b4b4.