Added reduce() function for FindWrapper

[DzikowskiW]

Resolves #62

[gnarf]

I really need to see a use case for this...

I'm having a hard time understanding why you'd want a reduce that does FindWrappers of the nodes... Map is an easy one for me, but reduce is getting a bit out there.

[mzgoddard]

Use the typeof check.

typeof initialValue === 'undefined'

[DzikowskiW]

@gnarf there is actually a decent example in enzyme's documentation. I think .map() is much more useful and if you want to keep preact-render-spy's API a bit more constrained, .reduce() is not a necessity, but otherwise it helps once in a while.

If we decide to keep this function, I will add a better README example. Let me know what's your decision on that.

[gnarf]

If we decide to keep this function, I will add a better README example. Let me know what's your decision on that.

I think I need to see that example to want to keep the function :)