Miniwdl

* Fix initialization of compound values with optional structs (563 jdidion)
* `miniwdl check`: add `awsBatchRetryAttempts` as known runtime entry (564 nh13)

`miniwdl run`

* Add support for attaching tasks to docker networks, via [runtime.docker_network](https://miniwdl.readthedocs.io/en/latest/runner_reference.html#task-runtime-attributes) and config `[docker_swarm] allow_networks` (555 jgadling)
* Add config option `[task_runtime] download_defaults` which is like `[task_runtime] defaults` but applies specifically to URI download tasks.

`miniwdl zip`

* Make archive file binary-reproducible, by sorting filenames and setting timestamps to an arbitrary constant (557 rhpvorderman)

New tool: `miniwdl zip`

Creates a zip archive of a WDL source file along with all imported source files. The zip includes a manifest JSON file in the style of [Amazon Genomics CLI's](https://aws.github.io/amazon-genomics-cli/docs/concepts/workflows/#multi-file-workflows) and, optionally, default inputs for the bundled workflow. `miniwdl run` can then operate on the zip directly (or zip extracted to a directory).


miniwdl zip https://raw.githubusercontent.com/broadinstitute/viral-pipelines/master/pipes/WDL/workflows/assemble_refbased.wdl
miniwdl run assemble_refbased.wdl.zip ...


Thanks rhpvorderman for prior art in [wdl-packager](https://github.com/biowdl/wdl-packager) and subsequent discussions informing this feature's design.

New tool: `miniwdl eval`

Evaluate a bare WDL expression given on the command-line; quickly trying out expressions to be used in WDL workflows, without running the whole thing.


$ miniwdl eval 'Int x = 42' 'select_first([None, x/2])'
21


`WDL` package

* Allow infix comparison between array and nonempty array constant (541 kinow)
* Fix spurious `WDL.load()` error after a previous `WDL.load()` operation failed in the same process (549 kinow)
* Don't require task `runtime{}` entries to be String-coercible

Fix runtime error initializing struct with `Map` member from `read_json()` (538 jmesterh)

* Allow mypy to recognize type annotations in `WDL` module (536 kinow)
* Allow privileged docker containers
* With configuration option `[task_runtime] allow_privileged = true` (environment `MINIWDL__TASK_RUNTIME__ALLOW_PRIVILEGED=true`)...
* and `privileged: true` is set in a task's `runtime {}` section...
* then miniwdl creates task containers with privileged capabilities (as in `docker run --privileged ...`).
* Not recommended, for security & portability reasons; but can enable advanced performance optimizations.
* udocker: invoke with `--allow-root` by default

* Add [udocker](https://miniwdl.readthedocs.io/en/latest/runner_backends.html#udocker-beta) container backend (beta)
* Fix race condition in docker status task monitoring (bkmartinjr)