title: Convert radian to degree in flutter expression
body: <p>I have an input expression from user, and there might be <code>sin()</code>, <code>cos()</code> and <code>tan()</code> in it, and also multi dimensional functions like <code>sin(60 + cos(30))</code>.</p>
  <p>I am using math_expression to evaluate the expression, but this package uses radian instead of degree. What should I do i f want to user degrees instead of radian?</p>