added documentation for mapControl directive

Have added docs for the `map-control` directive.

The example is commented out as does not run due to:
1. directive not in current release that website references and, more notably,
2. when adding a second controller to the `script.js` file for the example it throws an error on the call to `eval(cur.content)` **(base/example.js:62)** as it loops through the .js files. I am not quite sure what this is doing exactly so not sure how to fix it. Just need to add a template to `$templateCache` and define a controller for the `map-control` directive, is there another way I should be doing this?