Provide a way to describe the precedence of operations

[kevinbarabash]

This is so that we can avoid having to to:

return isMul(parent) || isPow(parent) || isDiv(parent)
            ? `(${result})`
            : result;

[tkosan]

@kevinbarabash many CASs enable operators to be defined by the user. Here are the primary operator definitions for MathPiper as an example:

MathPiper operator definitions