Add Autoclick Behavior

[ikreymer]

Fixes #81
Adds new autoclick behavior, which:

• Attempts to click on all 'a' elements as the default selector, customizable via opts.clickSelector option.
• Click on all links that are different page on same domain to trigger custom event handlers, requery all links in case DOM is changed due to dynamic navigation / custom event handler.
• Use heuristics to determine when link may just be a simple navigation (check event click handlers, check if target is set, check if element is visible, etc...)
• Use onbeforeunload to attempt to block navigation if link navigates away
• support custom selectors via

[tw4l]

Looks good and has been working well in testing, just one question