Lazy slides: lazyDistance setting

[blueyed]

Followup to #1338, adding a lazyDistance option.

Ref: #1338 (comment)

[syd2011]

coool

[blueyed]

Rebased on master.

@alvarotrigo
What do you think about it?

[alvarotrigo]

Looking good!!

Although that's lazy distance for slides.
Ideally lazyDistance will be for both, slides and sections.

Also, consider wrapping all of it in a function. Something like:

destiny = getDestinationsToLazyLoad(destiny);

Oh, and, the condition if( slide.length ) { seems to be there to only deal with the first slide of each section when landing in any slide coming from other vertical section.

Your code should also be applied when moving from slide to slide. So I believe it shouldn't be placed inside that condition.