matlab like array indexing

First version of the matlab style array indexing function proposed here: https://groups.google.com/forum/#!topic/numerical-clojure/zFjIl8zgX6M , to discuss the syntax.
Currently only supports getting elements, not setting them. Maybe another method for this would be the best way of adding it.
Supports all of http://www.mathworks.de/company/newsletters/articles/matrix-indexing-in-matlab.html except the setting of the selected indices.