This is the templating engine of WebPython.
Initializes the templating engine. _req is ment to be a copy of an HTTP request object, but is currently unused. It may be replaced, or implemented, in the future; I have not yet decided. _log_file is an optional argument string representing the location of the template engine error log.
Takes template file template_name (which must end in ".tpl") and substitutes for variables as explained in Section 3.1.4 (Templating). Returns the processed document ready for display.