Dask Bag examples

We currently lack dask bag examples in this repository. Two come to mind:

1. Read JSON data, and do some groupby aggregation with both Bag.groupby and Bag.foldby
2. Read text data and do some basic wordcount

For the JSON data it might make sense to add a dataset generation tool for nested records data, similar to dask.datasets.timeseries, and then use that to generate JSON data to disk, similar to how we generate CSV data in http://examples.dask.org/dataframes/01-data-access.html#Create-artificial-dataset.

We would then read the JSON data, and do some minimal processing.

For the text data I wonder if there is an online dataset we can download. I suspect that the complete works of shakespeare is around somewhere. We might do a simple thing like read, split, frequencies. Or we might do more complex work afterwards by bringing in NLTK, stemming words, removing stopwords, etc..