New Chameleon templating engine, engine is now configurable. We now have two configurable templating engines, the old Zope TAL templates (called zopetal in the config) and the new Chameleon (called chameleon in the config). A new config-option "template_engine" under [main] can take these config-options, the default is zopetal. Thanks to Cheer Xiao for the idea of making this configurable *and* for the actual implementation! Cheer Xiao commit log: - The original TAL engine ported from Zope is thereafter referred to as "zopetal", in speech and in code - A new option "template_engine" under [main] introduced - Zopetal-specific code stripped from cgi/templating.py to form the new cgi/engine_zopetal.py - Interface to Chameleon in cgi/engine_chameleon.py - Engines are supposed to provide a Templates class that mimics the behavior of the old cgi.templating.Templates. The Templates class is preferably subclassed from cgi.templating.TemplatesBase. - New function cgi.templating.get_templates to get the appropriate engine's Templates instance according to the engine name