- Make it possible to use :mod:`zope.component`
- Provide a concise list of all the available APIs in that module and
  link them to their in-depth descriptions.
- Fix several xref errors
- Add documentation for setHooks/resetHooks.

This also makes it possible to get useful help at the REPL or command
line:

$ python -c 'import zope.component; help(zope.component.getAdapters)'
Help on function getAdapters in module zope.component._api:

getAdapters(objects, provided, context=None)
    Look for all matching adapters to a provided interface for
    objects

    Return a list of adapters that match. If an adapter is named,
    only the most specific adapter of a given name is returned.

    .. seealso::
       Function `~zope.component.getAdapters` for notes, and
       `~zope.component.interfaces.IComponentArchitecture` for the defining interface.

And some internal links as well.

Remove mentions of 'IServiceService' from interface documentation, as that's not a thing.

ZODB 5.5.0 added an "import mock" to ZODB.tests.util (or "from unittest
import mock" on Python 3, which is in the standard library).  ZODB[test]
included the new dependency, but zope.component wasn't using that for
tests.

However, ZODB.tests.util.DB was just an import of
ZODB.MappingStorage.DB, so we can just as easily use the latter and
avoid the extra dependency.

And also in hookable.py

Do this using zope.deferredimport and zope.deprecation, two new
dependencies. This introduces a transitive dependency on zope.proxy,
but that was already part of the 'security' extra. zope.proxy runs
on pypy but it doesn't yet support making the C extension optional (https://github.com/zopefoundation/zope.proxy/issues/26)

Also drop the use of _compat._BLANK everywhere and just use the literal.

Drop pypy3.3-5.5-alpha

Sphinx needs Python 2.7 or 3.4+ to run, and this is a (really old)
version of Python 3.3. (Unfortunately the beta of PyPy3.5 does not
appear to be available.)