compose_yml: Support for working with docker-compose.yml files

This is a work in progress! Most of services: is supported, but I'm still refining the APIs as higher-level tools get build around this.

API Documention

Goals

docker-compose.yml is a very useful format, but it's hard to parse and transform correctly. This library aims to offer:

• High-level, type-safe APIs for anything you can find in a docker-compose.yml file.
• Parsing of individual string fields into real objects.
• Support for working with strings that might contain variable interpolations, and leaving them unparsed when necessary.
• Canonical representations of fields which may have multiple formats.
• Easy updates when docker-compose.yml gets extended.

Building

You can build this library using stable Rust version 1.11. But if you want to develop it, you will get much better error messages using a nightly build of Rust.

```sh

Install Rust stable and nightly using rustup.

curl -sSf https://static.rust-lang.org/rustup.sh | sh rustup toolchain install nightly

Build unit tests using nightly Rust.

rustup run nightly cargo test --no-default-features --features unstable ```

Sponsor

Part of the work on compose_yml has been generously sponsored by Faraday for use in their conductor tool, which orchestrates docker-compose for large, multi-pod apps.