Support for additional task types and outputs

[justin13601]

Right now we basically only support binary classification. This is ok for now, but we could aim to support more complex tasks:

• Ordinal regression
• Multi-class classification
• Multi-label binary classification
• Univariate Regression
• Multivariate Regression
• Sparse Regression
• Sequential decoding prediction tasks
• Time-to-event prediction tasks

Note this overlaps with #72

[justin13601]

We hope to directly support tasks whose labels cannot be reliably summarized as a single numerical value (ie., a sequential decoding task where we want to predict a sequence of outputs, such as future treatment sequences). For tasks that rely on time-to-event as a paradigm, labels can currently be manually extracted via the window start/end times (ie., subtracting start from end of your window containing your event of interest, and then bucketing appropriately post-hoc).

[mmcdermott]

To-do: merge this and #45