Solvers: Extending solveset

SymPy is a Python library for symbolic mathematics. Sympy has a powerful solve function that can solve a lot of equations, but due to its complex API and inability to give efficient output, solveset was implemented and is under development since 2014. A lot of work is needed to complete solveset. For transolve, Lambert solver needs to be completed. Handling modular equations will also be added. Proper use of Decomposition and Rewriting principle also needs to be implemented to solve nested trigonometric equations. Enhancing the set infrastructure to give simplified output for trigonometric equations is also needed along with integrating helper solvers with solveset.