Add option to disable inserting container

Sometimes it's useful to insert the container manually and use the map
function for the script only. Having an option to disable inserting the
div tag would be a nice addition.

* Add a new option 'no_container'
* Disable inserting the container if 'no_container' is true
Add a test for no_container option
Merge pull request #24 from smadeja/optional-container

Add option to disable inserting container