Move the section from `CONTRIBUTING.md` (which should only be policy) to
`DEVELOPER.md` (which should document developer tooling).
Consolidates the whole thing a bit, and adjusts for the now always
installed `git clang-format` hook. Also mentions clang-format's lookup
behaviour.
* `npm install` now does a full install; auxiliary installation steps
have been integrated into the `postinstall` script.
* Updated developer docs `DEVELOPER.md` accordingly; also added
instructions to dev docs for performing full tests (via `npm test`) --
same as those run on Travis.
* Reorg in tests so that JS tests can run without a Dart env.
Partly fixes#945 **under the assumption that when running JS tests
locally, `ChromeCanary` is the desired browser to use**. Note that CI
tests (Travis) still uses `DartiumWithWebPlatform` across the board
(Maybe because ChromeCanary isn't being installed?)
Fixes#1012.
Closes#1010
A first edition of `DEVELOPER.md` inspired from the angular.dart version
and expanded to include instructions given in this repos’ `README.md`
(which has been cleaned up and padded up).
Closes#946