Support for recursive extends (adjusted)

[HoldYourWaffle]

(supersedes #22)

As mentioned in #22, I need this feature in my project. Sadly @josephfinlayson never made the adjustments you wanted, so I did it.

Changes relative to #22:

• Added a complete & working test*
• Undid the irrelevant changes (like package.json)

There are 3 things I'm not 100% sure I did correctly:

• My test somehow requires an exact whitespace match (as far as I can tell), even though the original extends inherited layout test is almost the exactly the same.
• @josephfinlayson commented out line 91-96, but I can't figure out why you'd want to do that. Especially since it makes a test fail.
• Is the commit history clean enough? I used a merge to make sure @josephfinlayson got his credit, would a cherry-pick be better?

[HoldYourWaffle]

When I tried to use this in my own project it didn't work as I expected (throwing an error that definitely shouldn't be there), currently investigating.

[HoldYourWaffle]

After a lot of staring I think I found something that could lead to the cause. Keep in mind that I have no idea how reshape works beyond the code of this plugin, so there may be some (big) inaccuracies. I also don't have the code in front of me right now, so the variable names might be slightly inaccurate.

It seems like the tree modification logic (changing just the contents of nodes) is not sufficient to support this behavior. The merged tree is the same before and after the merge (this is something I didn't understand at all), so the already merged blocks are still passed on to the 'next layer'.

I'm way too tired to be doing this right now but I'll be looking at this again tomorrow.

[jescalan]

Let me know if you want to pair and walk through this whenever you're taking another look!

[josephfinlayson]

Also happy to pair!

[jescalan]

@josephfinlayson shoot me an email escalantejeff at gmail and let's set up a time 😁

[HoldYourWaffle]

I'm going on vacation soon so I won't have any time to look at this until somewhere next week.