Add elements property to Finder instance

[chrismwendt]

Previously, there was no way to get the elements in each match from the Finder instance, which made it impossible to count the matches, scroll them into view, etc.

This PR adds an elements property to the returned Finder instance. elements is an array of matches, where each match is an array of elements.

var finder = findAndReplaceDOMText(...);
console.log(finder.elements);