Symbolic computation with Julia (Symbolics.jl): Symbolic Root finding

Currently, Symbolics.jl has a Groebner basis implementation which is able to convert a myriad of symbolic expressions into multi-variate polynomials. This can be incredibly useful for solving functions for their roots, but to do so, a root finder for these generated polynomials must be implemented. Moreover, multiple users of Symbolics.jl have requested a symbolic nonlinear solver. As such, the project aims to complete the following: 1- Solve single variable polynomials (even high degree ones n ≥ 4) and multi-variable polynomials (over 2 dimensions or more) 2- Solve transcendental / other types of non-linear equations (highly requested: issues #961, #468, and #866) 3- Ensure that the implementation is well tested and well documented to make it more user-friendly and help out future contributors of the project.