Bazel support for Dart.

Bazel is a correct, reproducible, and fast build tool used internally at Google, and now open source, that provides a powerful and extensible framework for building software and maintaining code.

Large applications in Google like AdWords Next and AdSense have used Dart and Angular Dart in production with Bazel for a while, and now we want to share Bazel with the rest of the community.

WARNING: This package is highly experimental. While the underlying framework (such as BUILD rules and extensions) are stable, we're still iterating on a good stable solution for end users that are used to primarily working with pub and pubspec.yaml files.

Have a suggestion to make this better? File an issue.

The dazel package publishes a dazel command that takes an existing pub package and automatically generates a Bazel workspace: full of extensions, macros, rules, and more.