Grokcore-component

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- Compatibility for python 3l

- Python 3 doesn't support the directive ``zope.interface.implements``
any more and is required to use the ``implementer`` class decorator instead.
This version of grokcore.components provides its own
``grokcore.component.implements`` directive for both Python 2 and 3.
So this directive can still be used with the help of a grokker.
If you use grokcore.components >= 2.6 the new implementation will be used
while earlier versions used zope.interface.implements.

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- Introduce provideUtility, providerAdapter, provideSubscriptionAdapter,
provideHandler and provideInterface in grokcore.component. These by default
delegate the registration of components to the global site manager like
was done before, but provide the possibility for custom registries for the
grokked components.

- Fix the `global_adapter` to properly use information annotated by
``grok.adapter``, and using the IContext object if it was not
specified. (Fix Launchpad issue 960097).

- Add a ``key`` option to ``sort_components`` that behave like ``key``
options available on standard Python sort methods.

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- Fix the `global_adapter` directive implementation to accept an explicit
"empty" name for nameless adapter registrations (as it used to be that
providing an empty name in the registration would actually result in
registering a named adapter in case the factory has a `grok.name`).

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- Implement the generic (Multi)Subscriptions components.

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- The default values computation for the context directive and the provides
directive is now defined in the directives themselves. This means that where
the values for these directives is being retrieved, the "default_context"
function does not need to be passed along anymore for general cases.

Analogous to this, when getting values for the provides directive the
"default_provides" function does not need to be passed along in the general
case.

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* Made package comply to zope.org repository policy.

* Moved directives 'order' from grokcore.viewlet and 'path' from
grokcore.view to this very package.

* Tiny dependency adjustment: moved zope.event to test dependencies.

* Port from 1.x branch exclude parameter to the Grok ZCML directive.

* Port from 1.x branch the ignore of testing.py modules.