Implementation of the DIN99o color space

Implementation of the DIN99o color space, an optimization of the DIN99 color space, similar to DIN99d.
As glenn-sweeny already mentioned there exist a couple of modifications/optimizations of the DIN99 color space. I found that DIN99o has become increasingly important in color science, as the growing use of this color space in academic literature and, for example in the printing industry (Fogra Graphic Technology Research Association), show.

As glenn-sweeny already mentioned, if this implementation is not considered relevant enough for the project, I will happily keep it as a private extension.

Some references to DIN99o are:

* Georg A. Klein
[Industrial Color Physics](http://http://books.google.de/books?id=WsKOAVCrLnwC).
Springer Series in Optical Sciences, 2010. ISSN 0342-4111, ISBN 978-1-4419-1197-1.
(appended to README.md)

* Kittelmann P.
[Visuelle Beurteilung von kleinen und grossen Farbunterschieden und Beschreibung mit Farbabstandsformeln. Ph.D. Thesis](http://opus4.kobv.de/opus4-tuberlin/files/2520/philipp_kittelmann.pdf), Technische Universität Berlin; Berlin, 2010.

* Andreas Kraushaar
[Using modern colour difference formulae in the graphic arts.](http://www.color.org/events/colorimetry/Kraushaar_CIE-D1_CIEDE2000.pdf), CIE D1 meeting, Leeds 2013.