0.3.0

• Adds a EntryPointLookup.
• Adds a DelegatedLookup.
• Adds a ProxyLookup.
• Adds a proper resolution for system default lookup Lookup.get_default().
• Fixes issue with listeners registration disappearing immediately when using object-bound methods.
• Content of a GenericLookup can now behave like a Container (ie. you can do things like "obj in content").
• When an instance is not hashable, provides an alternative using id() of the object in order to be
  able to store it in a hash-based storage (set, dictionary).
• New syntactic sugar: call directly a lookup object as shortcut for the lookup method. Ie.,
  instead of writing "lookup.lookup(...)" you can now write "lookup(...)".
• Missing declared dependency in typing_extensions.
• Abstract methods now raise NotImplementedError