There appears to be a discrepancy between the description in the comments as well as [the documentation](https://www.emberjs.com/api/ember/3.0/classes/MutableArray/methods/removeAt?anchor=removeAt) and the typing itself. Since we can pass either a single index **or** a start and length, `len` should be an optional parameter (to handle the scenario where you just pass a single index).
* Fix typo Enumberable -> Enumerable
* Set return type to Enumerable of filter, reject etc to support chaining
* findBy value type should be any, not string
* Convert return type for Enumerable to NativeArray<T>
* Update RSVP to 4.0, to implement PromiseLike<T>.
- RSVP Promises can now be used with `async` and `await`.
- RSVP types now match what is in RSVP 4.0.
* Update ember-testing-helpers for fixed RSVP.
* Ember.js: correctly represent most of the framework.
- Capture the actual behavior of most of the framework, including computed
properties, custom getters and setters and the custom Object model more
generally, prototype extension via `.extend`, and the mixin pattern.
- Support the new modules API alongside the global API.
- Add extensive tests.
- Update inline documentation.
- Use the new, async/await compatible RSVP definitions.
* Ember/RSVP: drop .prettierrc files.
* Drop types/rsvp/assert.ts -- stick to just rsvp-test.ts.
* Fix ember-testing-helpers-tests on top of module itself.
* Fix RSVP import in ember-testing-helpers.
* Fix 'typeRoots', set ember-testing-helpers to use TS 2.4.
* Fix missing 'types' compiler option.
* Fix errors caught by dtslint.
* A few more tslint tweaks.
* Fix account link in ember-testing-helpers authorship.
* Disable strictFunctionTypes for Ember, RSVP.
* fix array.reduce signature conflict in ts@next
- Add default export and test code to RSVP, including sample code from
the RSVP library.
- Use imported RSVP types in Ember and ember-testing-helpers definitions.
- Set minimum TS version in RSVP, Ember, and ember-testing-helpers.
- Fix ember-testing-helpers header.
- Make RSVP a two-type-parameter type; update Ember typedefs accordingly.
- Update authors, definitions link in RSVP header.
- Add definitions for `computed.filter` and `computed.filterBy` methods.
- Add definitions for `getProperties` on Ember base object.
- Fix the `computed.map` definition to actually include the callback
- Fix the `run` method’s callback type.
