wrap events using other modules

[da-h]

API-proposal:

• (bf1e3e9) event-object should behave like a list of all events per module, e.g. events["moduleA"] should be a list of all defined events in that module
• (8d72615) (optional) introduce event.eventname.modules / event.eventname.fns for more granular control when using events directly
• introduce child modules to make it possible to collect / choose / merge events from other modules dynamically (see Dynamic Modules #21)

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Postponed:

• redefine event-representation for better readability
  • although overloading __repr__ is indeed possible. In my experiments a object with a __call__ is slower than first-class wrapper-functions.