Add mapbox-datasets-update-features with stdin or file input

[sgillies]

I'd like to make this possible:

$ mapbox datasets create
$ fio cat a.shp b.shp c.shp | mapbox datasets update-features $id

reading a GeoJSON feature sequence from stdin, or reading from a GeoJSON feature collection file.

$ mapbox datasets create
$ fio cat a.shp b.shp c.shp | fio collect > lolwut.json
$ mapbox datasets update-features $id lolwut.json

[rclark]

I intend to implement these functions:

• mapbox datasets put-features: stream in geojson, inserts and updates
• mapbox datasets delete-features: stream in ids, remove features
• mapbox datasets put-dataset: create/replace an entire dataset with whatever you pipe on stdin

I already wrote these out in a non-chunked, not-really-streaming fashion, and I hope to take a stab at using cligj to help here this afternoon / weekend.

[sgillies]

Stale.