add simple string/array commands

[m3brown]

Support simpler syntax for simple string and list commands.

Existing command format expects an object, where each object has a cmd that is either a string or a list

commands:
  foo:
    cmd: echo "bar"
  derp:
    cmd:
      - ls
      - echo "herp"

The new syntax supports the old format, but also supports commands that are simple strings or lists:

commands:
  foo: echo "bar"
  derp:
    - ls
    - echo "herp"

The old cmd format remains, it's necessary if the config needs to define additional fields (description, env, etc.)

[coveralls]

Pull Request Test Coverage Report for Build 1609318347

• 4 of 4 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.009%) to 99.242%

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Totals
Change from base Build 1609309093:	0.009%
Covered Lines:	262
Relevant Lines:	264

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💛 - Coveralls