[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
> doctests don't use unicode

unicode is not being used here it is ascii pretty printing, observe `use_unicode=False`. `pprint` is used to improve the readability of the example.