added findBy() and filterBy() methods 

I've added two related functions which operate on Array or Object collections:

1. `filterBy` - Allows you to filter down a collection to only those objects which have a matching name/value pair.

     usage:
     ````php
     Object::filterBy($collection, $property, $value, $comparisonOperation = "eq");
     Arrays::filterBy($collection, $property, $value, $comparisonOperation = "eq");
     ````
1. `findBy` - Very similar to *filterBy* but assumes that only one result should be returned and therefore *unpacks* the surrounding array. 

     usage:
     ````php
     Object::findBy($collection, $property, $value, $comparisonOperation = "eq");
     Arrays::findBy($collection, $property, $value, $comparisonOperation = "eq");
     ````

> note: If the filter operation actually does return more than one result, findBy will take the first object in the resulting array of objects.
Can you reduce some of the repetition here ?