Given the lengths of the 3 sides of a triangle as inputs, calculate the area of the triangle using Heron's Formula. For example, a 3-4-5 triangle has an area of 6 square units. See Wikipedia or Khan Academy for details. Another example: a = 4, b = 13 and c = 15 area = 24
https://en.wikipedia.org/wiki/Heron%27s_formula
