Fixed possible TypeError while sending multipart emails.
(Zope 2.11 and 2.10 are not affected.)

- Left behind the old module / names for backwared compatibility.

Removed the deprecated ``five:containerEvents`` directive, which had been a no-op for quite a while.

Removed Products.Five.fivedirectives.IBridgeDirective - a leftover from the Interface to zope.interface bridging code.

Marked the ``<five:implements />`` as officially deprecated. The standard ``<class />`` directive allows the same.

Turns out zope.cachedescriptors was only a test dependency of formlib, which we don't care about anymore.

 * mention plone.recipe.zope2instance, which is more convenient for people
   starting from scratch

 * correct the name of the mistyped 'log' subdir.

 * more explicitly mention that the zope.conf excerpt provided here is just
   that: an excerpt, and not a complete minimalistic zope.conf.

Use new zope.traversing, which allows us to get rid of zope.password, zope.principalregistry and zope.securitypolicy.