Added a 'lambda' to gray in color.rb to allow definition of a color specific function.
Added 'arc' to shape.rb.
Implemented 'arc' in swt/shape.rb (converts radians to degrees).
Small changes to simple-arc.rb to make it match example image referenced in source file.
Possible issue with change in simple-arc.rb to use @app.width / @app.height as self.width and self.height always seem to be 0 - need to check how this works.