Fix issue 175

[galleon]

This commit change the way a Box action is discretized.
It is inspired from the gym.spaces.Box.sample method. For unbounded spaces it builds on the quantile distribution of the Cauchy distribution (using a scale of 1).
An alternative could be derived from the logit function: log(1+p) - log(1-p) for example. But the current implementation has a larger spread.

[nhuet]

Hi. The first commit "Removing need for GH_ACCESS_TOKEN" should not be part of this PR. For the remaining, it seems ok for me but I let more qualified people decide about what the Box space should look like.