Remove redundant "On" word in event hook natives.
Require callback ID when unhooking an event.

The event manager need to know which callback to unhook, assuming we're not going to allow double-hooking events in the same module.
Add generic event hook native in the event manager.
Update event manager documentation.

* Add technical user stories.
* Update implementation guidelines with info about forwards, direct events and bootstrapping.
Simplify some parameter names of natives in the module manager.

* Remove ID suffix in moduleID and featureID parameters. They are redundant because modules and features are always identified by their ID, and the tag indicates that they are IDs too.
Remove module dependency natives.

We're not going to support module dependencies. Instead modules should declare dependencies on specific features, regardless of which modules that implements it.
Update module manager documentation.

* Add technical user stories.
* Update info about dependencies, module IDs and bootstrapping.