Image Functions: Colour and image processing routines

This class provides an helpful collection of colour and image processing routines.

It can:

- Can the colour space to and from RGB, HLS and HSV formats
- Convert to and from an RGB array and HTML HEX values
- Retrieve the colour of a pixel and return it as an RGB array
- Compute the distance between two colours
- Determine the current GD library version used by PHP by parsing phpinfo() output
- Grey scale an image
- Sepia tone an image
- Apply a threshold limit to an image
- Return a range of colours from a start colour to an end colour in a given number of steps