Move oil to unpkg.com

This is the fourth minor release. See below for details.

New Features

[OIL-268] Use unpkg.com as hosting service for open source version of oil.js

Bug Fixes

none

Configuration changes

publicPath: default is now "/@ideasio/oil.js@{version}/dist/latest/".
poi_hub_origin: default is now "//unpkg.com".
poi_hub_path: default is now "/@ideasio/oil.js@{version}/dist/latest/hub.html".

Chores

none

Documentation Changes

none