Render formula: Render mathematical formulas as images

This class can be use to render mathematical formulas as graphical images.

It parses a formula with constant and variable values combined with several possible mathematical operations.

Currently it supports formulates using the operations: addition, subtraction, multiplication, division, and functions like square root, sin arc sin, cosine, and power.

Then it renders the given formula in an GD library image. It uses a given True-Type font to render the formula characters.

The class returns a GD library image resource handle that can be used to output the formula image in any format supported by the GD library.