Fixed #30: "includes" flag in custom structures

First, it is now possible to give to domino.struct.check as third argument an object containing flags. Currently, the only recognized flag is "includes", and it allows non-specified keys to be used additionally to the ones required.

Also, any flag given to a custom structure when added is now also given to domino.struct.check, so using this new "includes" flag in a custom structure works.
Fixed #27: fixed "force" property parameter

It is now possible to set the flag "force" to true in a property to force the descending events to be triggered, even when the new value is not different from the old one.
Fixed #28
Fixed #23: referencing modules with unique IDs

It is now possible to specify an id when creating a module: The method "addModule()" can take as third argument an object with some options, and this is where the string id can be specified.

It basically works as instances id:
  - It is not possible to reference two modules with the same id.
  - It is possible to call the ".killModule()" method with the id instead of the module itself.
  - When an id-ed module is killed, it is possible to reference modules with its id again.
  - It is possible to access a reference to id-ed modules through the method ".modules()" (just like the global method ".instances()")
Fixed #32
Fixed #26: descriptions management + help() method

The "description" attribute is now recognized for shortcuts, hacks, properties and services. It is still optional, and has to be a string if specified.

The global instance also has from now a "help()" method, to see these properties. See the method documentation or the unit tests to learn exactly how it works.
Fixed #29: Version info in development file
Added .help() unit tests in test/unit.misc.js
release v1.2.4