Change LessCompiler input from File to URL.
Created LessSource to represent either a File or a URL source.
LessSource now exposed as an input type to the compiler, and now
collects lastModified (and latestModified) times and a collection of
the resources that were imported.

This will enable a caller to have more control over the source, and to
observe which files were used and what their lastModified times were.
So the caller can implement caching.
Initial implementation of colour functions.

Adds support for alpha into a subclass of ColorExpression, which then
uses
the rgba() format to output to the CSS.
Tidy source code

Correct indentation, and undo unintentional changes to imports due to an Organise Imports run in Eclipse.
Tests referenced incorrect resources (swapped)
ColorFunctions: create constants for all of the functions as a sign of optimism
Color functions: implement rob, rgba, hsl, hsla, argb.

The implementation of ARGB uses a new node called Anonymous. I copied this approach from the less.js source.
Mixin test-case output tweaked to match now implemented rgba function
Color functions: more functions implemented

Hue & spin don't quite match the sample yet.
Color functions: use HSL functions from less.js

Still doesn't resolve hue not matching in functions-color.less -> .css. I have also tried another HSL->RGB->HSL converter and got the same result, so this example may not be correct. I will check to see how less.js handles it.
Color functions: implement saturation, lightness, red, green, blue, alpha, luma, mix, greyscale
Merge branch 'refs/heads/color-functions'