Pixel ratio tests
Pixel ratio implementation

- added Imager.transforms to let room to customise things further on
- replacing {pixel_ratio} pattern in `data-src` URI
`pixel_ratio` -> `pixelRatio` as method name.

Also made the pixel ratio computation executed once, not every time an image is replaced (because it is not supposed to change within the lifecycle of a page).
Setup to publish as `imager` on `npm` and `bower` registries.

- list of authors
- licensing
- created bower package
- made `imager` available for publication in npm (it is relevant to use it to host web component on npm)
- created the AUTHOR file for npm authors list
Codestyle consistency
Merge pull request #27 from oncletom/feature-pixel-ratio

[READY] `data-src` + pixel ratio variable
Testing width interpolation
Force sorting to avoid unordered sizes.
Using a Hashmap instead of an array of objects.
Safer way to check array type
Merge pull request #23 from oncletom/feature-data-src-interpolated

[READY] `data-src` + value interpolation
Testing internals and combinations of elements with/without options
Removing $ from the global namespace to avoid conflicting with the internal dollar and tests
Handling images in fixtures
First draft of implementation, not working yet.
Fixed HTML issue breaking tests
Cleaning fixtures is a good idea.

And making sure we detach any HTML/Array-like collection.
`(Array.prototype|[]).slice.call` -> `applyEach` w/ callback function
Fixed merge issues (fixtures and duplicate `afterEach` block)
`returnFn` -> `returnDirectValue`