v0.4.0-alpha.3

v0.4.0-alpha.3: Allow sources be created without a `name`

v0.4.0-alpha.2: Add `name` to `dataset:Args`

This allows setting a dataset name at creation time.

v0.4.0-alpha.1: Port to async & add bigml-parallel tool

This version of the Rust `bigml` client now uses nightly Rust (and tokio
1.x) to provide async APIs. This breaks BigML source upload abilities
because BigML doesn't yet support `Transfer-Encoding: chunked` without
`Content-Length:`.

This release also includes a new `bigml-parallel` CLI tool that can be
used to execute a WhizzML script in parallel over multiple sources or
datasets, outputting the BigML execution JSON returned by each run. The
degree of parallelism is controllable, and the input resource IDs can be
streamed on standard input.