[READY] Refactoring Plan

[thom4parisot]

Finally proposed as #49

This PR is intended to be kept open as long as the refactoring is running.
All refactoring PR are going to be based onto this branch.

Feel free to cherry pick!

Imager.js

• [x] data-src format – #21
• [x] OR data-src + availableWidths as a function – #33
• [x] data-src + Value interpolation – #23
• [x] data-src + Pixel ratio variable – #27
• [x] Constructor API – #22
• [ ] Constructor options – #?
• [ ] Update API – #24
• [x] Triggering on Events/Manually – #25
• [ ] Delaying width calculation and src replacement – #26

  Strategies

• [ ] Strategy implementation (as config or build file) – #28
• [x] Replacing the placeholder by a responsive image – this is the actual way of doing things
• [ ] Enclosing the responsive image in the placeholder – #?