Base ID of Heapbox on ID of selectbox it's replacing

The random ID generated was pretty pointless for styling purposes. It makes more sense to base the ID on a prefixed version of the original select's ID.
Merge pull request #9 from ChezFre/patch-1

Base ID of Heapbox on ID of selectbox it's replacing
Merge branch 'master' of https://github.com/FilipBartos/heapbox
Remove trailing comma in object definition
Updated README