0.2.3

In this release we include some internal naming changes, additional features for the geometry module (in particular geometry::spaces) and the addition of a new domain that interacts with the OpenAI gym via a python interpreter instance. At the moment there are some unresolved changes needed to better handle infinite dimensions (which are common in the OpenAI gym - see #24), but one can run experiments and upload results to the OpenAI leaderboard.