Adding eslint as dev dependancy ?

[Nalca]

Hello,

After fixing some undeclared vars in src/Filter/Fold.js (see #225) , I tried using eslint to find some errors and ...

More than 40 files use undeclared files.
You can be sure it's gonna explode if you use this code in strict mode ("use strict";). It did exploded for me when i used the folding filter.

This project should use a linter, even if it's not used in the build process. Just to find all those silly things that can throw Errors when executed.

[Viglino]

I've publish a bulk of fixes 😄 and eslint only return error on jQuery as we are removing it from the project asap.