General purpose task for building external modules
Parse examples and build external modules on install
Add wrapper for the RBush
Set type for `ol.ext.*`
Minimal typedef
Work with modules that assign to exports

CommonJS style modules will either assign `exports` to `module` or will assign properties to `exports`.  This allows us to work with either style:

    module.exports = Foo;

or

    exports.Foo = Foo;

Support for additional properties that are assigned to `exports` (or non-function values assigned to `module.exports`) will likely take additional typedef work in the wrapper.
Merge pull request #2867 from openlayers/module

Support for importing CommonJS style modules (like rbush).