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 - Only run-script on pods enabled in current target

Add run-script command (faradayio#71)

* Add run-script command

* Don't swallow executable name on `run-script`

* Fix warnings

* run-script will require new version, 0.3.0

* Add CLI test for Project::from_current_dir to fix build

* Just bump patch version

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.

v0.1.10: Preliminary dc.yml version 2.1 support & Windows tests pass

We should now have some basic support for many of the features which
will be present in the `docker-compose.yml` format version 2.1, and all
our unit tests are green on Windows.

This does not necessarily mean that Windows works as well as Linux and
Mac, but it should usable for many tasks.  Bug reports and PRs are
eagerly welcome!

v0.1.9: Run hook scripts in project root directory

This is a quick fix for an annoying bug that I don't want to hold up on
other ongoing work.

v0.1.8: Fix builds on older stable Rust

There was an unexpected build failure on Linux for 0.1.7 because it was
using an older version of Rust to make the static release binaries than
it was using to run the regular tests.

This release should restore compatibility with the older Rust we're
using to make binaries (which I also need to update).

v0.1.7: up --init, rm -fv, better status, several fixes

Third-party contributors to this release include Jeremy White, who fixed
a test suite failure on the experimetal Windows port and provided
extensive data about Docker on Windows, and Seamus Abshere who
contributed a glossary of `cage` terminology.  Thank you for your
contributions!

Bug fix:

- The `cage test` command now works correctly again, and a comprehensive
  integration test suite has been added to prevent further regressions.

New features:

- We now talk directly to the Docker daemon for several new features
  using the `boondock` library, a `cage`-specific fork of the very
  useful `rust-docker` with partial support for Docker 1.12 and Windows.
- `cage up --init` can now run task containers to initialize databases
  and other services on first run.  This has a built-in port scanner to
  make sure your containers have had time to spin up.
- The `rm` command now supports `-f` and `-v` options similar to those
  of `docker-compose`.

v0.1.6: Fix Linux releases on latest Travis setup

Docker had stopped working on our Travis builds, which meant we didn't
build any Linux binaries.  This release should fix that.

Internally, we've also fixed many, but not all, unit test failures on Windows.