[WIP] Data Keyword

Created by: wilsonmr

I will add some more description here later

I basically realised straight away that I actually don't know a good way to be able to parse both experiments and data and produce the same object - with a warning for the former and in the case that both are missing raise the correct exception that data keyword is missing

I found that this does some of the right things but having both a production rule and a parse for the same thing seems like I'm not using this in the way it was intended.

Any suggestions? Being able to process experiments is purely from a backwards compatibilty persepective