Fs tree facade

[stefanpenner]

playing around with a more complete FS facade \w change tracking.

• more tests
• ordered changes
• reviews
• docs
• how to deal with (try and figure out if we do) lazy materialization e.g. linkRoots and some merge-tree opts. I think funnel can learn how to do this efficiently.
• ???
• applyOutput @krisselden

tree.applyOutput(tree => {
  tree.writeFileSync('foo');
  tree.mkdirSync('apple');
}); // diff, and "cleanup" files not in this transaction.

• support directories in writeFileSync @krisselden

Fix #59

[stefanpenner]

use: https://www.npmjs.com/package/chai-files

[stefanpenner]

This is great work, the resulting research lead to several improvements in the ecosystem. This PR itself though should likely be closed, as we will most likely not be actively pursuing this approach in the near term. Additionally the code-base has changed drastically, if we do explore this again it will look very different. We will still have this PR around for history, and context, but we closing it seems appropriate.

[stefanpenner]

Knowledge from this has been used to implemented by https://github.com/broccolijs/fs-merger + https://github.com/broccolijs/broccoli-output-wrapper which is in mainline broccoli now. Further work is possible, but should likely be explored independently of this project. :)