circleci: anchors and aliases

[vsoch]

I'm just figuring out that yaml has these definitions called "anchors" and then "aliases" that can be used together to define a function (or set of configuration values) and then reference / reuse across a build workflow! For example, I might set a default:

defaults: &defaults
  docker:
    - image: docker:18.01.0-ce-git
  working_directory: /tmp/src
  environment:
    - TZ: "/usr/share/zoneinfo/America/Los_Angeles"

and then reference it:

version: 2
jobs:
  setup:
    <<: *defaults
    steps:
      - run:
          name: Test if the user has defined the repository name
          command: apk add --no-cache pigz python3

using this for any repeated code would be ideal to clean / simplify the config files! I think we would also want a way to add a variable input to a function, I'm still looking into / testing if I can do this.