v0.3.0-alpha.2: Fix `cage status` & `vault` everywhere

`cage status` should now work again. And the `vault` plugin should be
enabled on all platforms.

v0.3.0-alpha.1: Update to modern Rust

This version should be compatible with the 0.2.x series, but it contains
extensive updates under the hood. Experimental.

v0.2.7: Add support for `ulimits`

v0.2.6: Add support for `ulimits`

v0.2.6: Add support for `target`

This includes (very) partial support for v2.4 docker-compose.yml files.

v0.2.5: Hide annoying warnings

Thank you, @camjackson!

v0.2.4: Build URLs with subdirectories & dependency updates

@camjackson has added support for using sudirectories inside git repos
in the `build:` URL.

This release also updates most of our dependencies, including `serde`,
to much more modern versions, and restores the Linux binary builds that
were missing from v0.2.2.

v0.2.3: Miscellaneous improvements

From @camjackson:

- Support for UDP port mappings!
- Only `cage build` will actually run Docker builds. So no more
  accidental builds when running `cage up`.

From @dkastner:

- A new `cage run-script` command, which makes it easy to run
  alternative scripts defined for particular images. One use case of for
  this would be a container-specific script to notify Rollbar of the
  deployment of each container.

From @emk:

- `cage new` now uses the Alpine version of PostgreSQL in new projects.

Note that the projects generated by `cage new` may fail with PostgreSQL
permission errors on `cage up db --init`, thanks to issues in the
upstream PostgreSQL images. We want to fix this, but getting these other
fixes out now is a higher priority.

v0.2.2: run-script only on pods enabled in current target

Previously, the run-script command operated on all pods/services. In this release, pods and services are scipped if they are disabled in the current target via metadata.

v0.2.1: run-script command

The run-script command will execute a named script for any configured service. These scripts are configured in pod metadata files.

v0.2.0: Better `run` subcommand

The `run` subcommand can now run arbitrary services in arbitrary pods,
by popular demand.  This may be a breaking change in case of pods and
services with the same name, so I've bumped the version number.

There are some other minor ergonomic improvements and warnings for
several subcommands.