WIP: Realtime decoding

This is being built on top of @mluessi's PR: https://github.com/mne-tools/mne-python/pull/382. First attempt at building something is a simple decoding example using SVM. My plan is to move much of the code into functions such as rtSVM. It seems to work, but I am surprised at uniformly 100% accuracies - either something wrong with the code or we need to change the categories being decoded.