Add the `plist` cookbook
Add the `plist_test` cookbook and a spec
Add why-run output of XML differences for when plists are about to change
Change the plist `dict` key insertion procedure so that keys remain lexicographically ordered
Add support for appending distinct values to nested plist `array`s via the `PlistFile#push` setter
Add support for the plist `date` data type
Add the `:create` action to the `plist_file` LWRP