removed dependencies on global state in loaders.cache
replaced add_to_builtins with default_engine.add_to_builtins; TemplateEngine.add_to_builtins accepts module name
working state -- rewritting test_templates
working state
working state
working state (reordered methods)
working state
working state
rewritting test_templates -- working state
removed dependency on default_engine in SsiNode