[WIP] Rewriting the Univariate Solver

This PR aims to rewrite a cleaner and robust univariate equation solver.
- [ ] Univariate
    - [x] polynomial
    - [x] rational
    - [ ] trigonometric
    - [ ] functions with exp and log
- [ ] Multivariate
Probably, this should go to the Parameters section of the doctsring.  See [this](https://github.com/sympy/sympy/wiki/Writing-documentation).