text: Title: feature request: add describe support for new reduction models
  Body: [This](https://github.com/ContextLab/hypertools/pull/136) pull request adds support for a wide range of new data reduction models.  However, there aren't equivalent `describe` methods like [this one](http://hypertools.readthedocs.io/en/latest/hypertools.tools.describe_pca.html#hypertools.tools.describe_pca) for those new models.
  
  I propose changing the name of `hyp.tools.describe_pca` to `hyp.tools.describe`, and then adding a `model` flag to specify the reduction model (default: either PCA or IncrementalPCA depending on how we resolve [this issue](https://github.com/ContextLab/hypertools/issues/134)).