#5 Allow users to create there own functions to use in \solver

[loserpenguin15]

Provide some means for a user to create there own functions that they can later use in computations.

an example would be

\defineFunction{A}{x,y}{x^y} % A is the function name, x,y are the input variables, and x^y is the function to evaluate
\solver{A(2,3)} = \answer % will result in 8.