We recently merged a discretizing transformer into the discrete branch (see diff between that branch and master). Before merging it into master, we'd like it to be able to one-hot encode the output by default.

I propose that we have a parameter encode='onehot' by default which produces a one-hot encoded sparse matrix, with other options 'ordinal' (for the current default output) and encode-dense which produces a dense version of 'onehot'.

To dear contributor: Make sure to submit a pull request to the discrete branch.