Add omit input, deprecate others

[robherley]

The omitFooBar inputs are getting a bit repetitive, so instead of:

omitUntestedPackages: true
omitSuccessfulPackages: true
omitPie: true

It's just going to be:

omit: |
  pie
  untested
  successful

Or:

omit: 'untested'

etc

The other inputs previously documented will still work. Also adds new things to omit: stderr, pkg-tests, and pkg-output