Update license file with copyright holders

I went with whatever was in https://github.com/emberjs/ember.js/blob/master/LICENSE due to this ...

Update Ember.js compatibility info

Add Ember.js 3.8 and 3.12 to ember-try and update min version in README.md

Test addon against Embroider

Drop Node.js 13 support and add Node.js 14

Update to Ember 3.5

Unpins ember-compability-helpers

update lockfile to fix node 10.x dep

avoid ordered-set deprecation

Update ember-cli and get property test coverage for beta & canary

updated ember-compatibility-helpers version.

Avoid shipping duplicate implementation.

Using ember-compatibility-helpers' `gte` allows us to avoid shipping any
additional code in vers...

Update to the latest ember-cli blueprint.

Update README

Remove unused `.gitkeep` files

ember-try: Use `versionCompatibility` property

Add CHANGELOG

Cleanup npm dependencies

package.json: Add project metadata

Add more unit tests

Import JSDoc comments

Rename to `@ember/ordered-set`

Import OrderedSet class from ember.js

ember-try: Add missing `useYarn` flag

Use yarn instead of npm

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