Red-Black Tree Deletion

After implementing deletion for my [red-black map](https://github.com/LeoWoerteler/xq-modules/blob/master/src/main/xquery/modules/ordered_map/rbtree.xqm), I also ported it to yours, as you mentioned in a [mail](http://x-query.com/pipermail/talk/2013-November/004193.html) that you would like to have one. I actually like this implementation better because it gets away without the additional colors introduced by [this algorithm](http://matt.might.net/articles/red-black-delete/).

I omitted the fuzzy test query that I used to debug the implementation because it uses [XSLT 3.0 maps](http://www.w3.org/TR/xslt-30/#map). I can add it to the pull request if you are interested.