Add support for batch builds

[tscully49]

I can't seem to find a way to run this against a codebuild batch job. This functionality would be great!

Example buildspec.yml

version: 0.2

batch:
  build-graph:
    - identifier: templates
      buildspec: templates/buildspec.yml

[tomaszdudek7]

Any hacks to make it work?

[digglife]

Is this a wontfix issue?

Would be nice if we can test batch locally.