Going all prototype baby
Going all prototype baby

Why ? Seemed the only true way to have multiple instances of Lazyload
and keeping a small constructor.

Other options were:
- An enormous constructor wrapping all functions declarations and private variables
  all the way down. See previous commit.
- An enormous constructor wrapping this.fnName = function()
- A small constructor and lots of external functions declarations but
  then you have to pass arguments everywhere (imgs, img, lazyAttr, etc)

Now, I needed this for the next features of the Lazyloader: multiple
instances, different containers (not just body), horizontal and vertical

Closure compiler advanced eats this shit very well (1.2kb) minifying prototypes etc.

gmetais/lazyload,gmetais/lazyload,vvo/lazyload