Z3c.pagelet

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- Moved z3c.pt include to extras_require chameleon. This makes the package
independent from chameleon and friends and allows to include this
dependencies in your own project.

- Upgrade to chameleon 2.0 template engine and use the newest z3c.pt and
z3c.ptcompat packages adjusted to work with chameleon 2.0.

See the notes from the z3c.ptcompat package:

Update z3c.ptcompat implementation to use component-based template engine
configuration, plugging directly into the Zope Toolkit framework.

The z3c.ptcompat package no longer provides template classes, or ZCML
directives; you should import directly from the ZTK codebase.

Note that the ``PREFER_Z3C_PT`` environment option has been
rendered obsolete; instead, this is now managed via component
configuration.

Also note that the chameleon CHAMELEON_CACHE environment value changed from
True/False to a path. Skip this property if you don't like to use a cache.
None or False defined in buildout environment section doesn't work. At least
with chameleon <= 2.5.4

Attention: You need to include the configure.zcml file from z3c.ptcompat
for enable the z3c.pt template engine. The configure.zcml will plugin the
template engine. Also remove any custom built hooks which will import
z3c.ptcompat in your tests or other places.

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- Change request interface in pagelet adapter signature e.g.
(context, request, pagelet). Switch from IBrowserRequest to IHTTPRequest.
This allows to use the pagelet pattern for jsonrpc request which doesn't
provide IBrowserRequest. Also reflect the changes in configure.zcml

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- ``zope.app.pagetemplate.metaconfigure.registerType`` was moved to
``zope.browserpage``, so it gets now imported from there.

- Dropped test dependency on ``zope.app.security``, it is no longer
needed.

- Using python's ``doctest`` instead of deprecated
``zope.testing.doctest[unit]``.

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- Fix untrusted redirect to google.com in tests. It's now forbidden by default
by newer zope.publisher versions.

- Change ``zope.app.publisher`` dependency to new ``zope.browserpage``, as it
has much less dependencies.

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* Got rid of dependency on ``zope.app.component`` by requiring
``zope.component >= 3.7``.

* Removed hard dependency on ``zope.formlib``: the pagelet forms now
only get defined when ``zope.formlib`` is available. Tests still
depend on ``zope.formlib``, so it got a test dependency.

* Made sure long_description renders fine on pypi.

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* Allow use of ``z3c.pt`` using ``z3c.ptcompat`` compatibility layer.

* Add support for context-specific layout and content template lookup,
using (view, request, context) discriminator. This is compatible with
context-specific templates introduced in z3c.template 1.2.0.

* Don't do rendering in pagelet's __call__ method when request is a redirection.

* Add sphinx-based HTML documentation building part to the buildout.