Add option to ignore hidden markers

[maechler]

I added an option to ignore hidden markers when creating the cluster in the function "createClusters_".
The default value is set to false, which reflects the current state.

[Remo]

I think I've had a similar problem: #44
My approach is a bit different though. I'm adding all marker and only return those that are visible.
That way I can dynamically change the visibility of a marker. Is that something you've tested, maybe I've missed something in your change.

[maechler]

I just had a look at the code I wrote then, I am manually calling repaint() on the marker clusterer object after I changed the visibility of the markers. I do not think that is a big problem, apart from that it works like a charm.
Does your solution work without having to call repaint() ?

Anyways..it does not seem like this repository is actively maintained..

[Remo]

I see! I think my change did the same, I just needed more code ;-)
I'm thinking about forking this repo and merge some of the pull requests.

[Remo]

@maechler going to merge this in our fork over here gmaps-marker-clusterer/gmaps-marker-clusterer#7

[maechler]

Great! thanks. It's nice to see that the code is now in a repository where it can be maintained!

[krisgale-zz]

just added it to a work-in-progress... and this version works great!
@brendankenny @moiarcsan @maechler ship it. it's a small but Very useful addition.