Added pluggable random number generator

[davidtinker]

Hi Jason. Thanks for your cool library. I needed to be able to reproduce word clouds so I added a pluggable random number generator. Example usage:

var makeRandom = function(seed) {
    return function() {
        return (seed = (seed * 9301 + 49297) % 233280) / 233280.0; 
    }
}

var random = makeRandom(123);

var layout = d3.layout.cloud()
    .random(random)
    .size([width, height])
    ...

[davidjb]

Something like would be fantastic -- being able to re-create word clouds would be an extremely useful feature for consistent output on a page or being able to save/replay certain word clouds using just the seed number.

Is this able to be accepted?

[shanewholloway]

+1 — I (re-)implemented this patch in the d3-cloud library before I discovered this pull request.

It worked fantastically using a Mersenne Twister implementation.

[ebi]

Would be very nice to see this merged.