Change the format of module instantiation

Currently, it's only possible to create modules at the leafs of the
namespace structure. This CL lifts that restriction.

Get rid of "use strict" in many cases.
Merge branch 'dev' of https://github.com/evancz/Elm into dev
New convention for storing module values, fixes bug

Before it was not possible to add values to anything except leafs of
the namespace structure.