Document installation of phantomjs via MacPorts.
Merge pull request #221 from sahilm/patch-1

Document installation of phantomjs via MacPorts.
Also call #to_s on value passed to #set when dealing with file input to ensure the correct type is passed over the wire to PhantomJS.
Spec for setting a file on a file input element with Pathname.
Added an entry to the Changelog for #215.