Changes to get `composes` working with css-modules and our build system

[tomdye]

Type: bug / feature

The following has been addressed in the PR:

• [x] There is a related issue

• [x] All code matches the style guide

• [x] Unit or Functional tests are included in the PR

• updates postcss dependencies

• adds postcss.config file

• adds test for non json-format exports (composes output)

Resolves #166

[tomdye]

@kitsonk what do you want me to do re. the file showing as uncovered even though it's now clearly tested?

[kitsonk]

what do you want me to do re. the file showing as uncovered even though it's now clearly tested?

Find out why it isn't being covered? It is being instrumented, but the tests don't actually seem to be covering it. https://codecov.io/gh/dojo/cli-build/pull/167/diff

[agubler]

@tomdye can you resolve the conflicts please 👍

[kitsonk]

Also, let's not worry about the coverage for this too... so if we rebase than I would be comfortable with a merge.