Teach bindEventHandlers() to use definable option for anchor elements

Addition of an "anchors" option which defaults to "a" and is used by the bindEventHandlers() function.

By default, smoothstate will operate as the author intended (binding to all links other than those matching "blacklist" selector string), but if user provides their own "anchors" value will allow them to bind smoothstate to subset(s) of links within their project.
Merge pull request #12 from phpMagpie/patch-1

Teach bindEventHandlers() to use new "anchors" option