Eat your vegetables - Broccolification

OK, so this is my stab at #93. Building the different versions (AMD, CommonJS, standalone) via `broccoli build dist` is now possible. This is my first time using Broccoli so the `Brocfile.js` is kind of a mess and looks accordingly. I am sure that there is place for improvements so keep the feedback coming!

~~I [changed](https://github.com/pangratz/router.js/commit/f369b721cc490491222b0437a5135a74a76f4a0c) the import statements in `lib` and `test/tests`, so they are relative now. This can be extracted into a separate PR I guess ...~~  see https://github.com/tildeio/router.js/pull/96#issuecomment-40910609

There is still an issue which needs to be resolved: The contents of `dist/router.js`, `dist/router.amd.js` using `broccoli` are the same like the ones, using `grunt build` before. But it seems that the CommonJS version in `dist/commonjs` now includes more files than before: `dist/commonjs/router/handler-info/*` and `dist/commonjs/router/transition-intent/*`. I don't know, but have they been "forgotten" in previous builds or should they not be there?

I leave some comments in the `Brocfile.js` where I'm uncertain how stuff can be handled better ...

:deciduous_tree:

**TODO**

- [x] simplify `Brocfile.js`
- [ ] add some documentation to the README
- [x] ~~fix issue with module naming in https://github.com/rpflorence/broccoli-es6-module-filter, see [here](https://github.com/pangratz/router.js/blob/95d892bdee610cb604389d5ff58084d830372e57/package.json#L31)~~ will be addressed upstream
- [x] use released version of `broccoli-wrap` instead of `master`, see [here](https://github.com/pangratz/router.js/blob/95d892bdee610cb604389d5ff58084d830372e57/package.json#L30)
- [x] ~~Use `bower` for dependencies ...~~ will be addressed in a separate PR
- [x] ~~check if https://github.com/rpflorence/broccoli-dist-es6-module can be used. The last time I tried, there were some errors. Will try again ...~~ will be addressed in a separate PR