was causing tags to compile with
  case-insensitive names, thus messing up
  custom <%call> names. [ticket:108]

- removed unnecessary attributes from DefTemplate.
- added ModuleTemplate class, which allows the construction
of a Template given a Python module generated by a previous
Template.   This allows Python modules alone to be used
as templates with no compilation step.   Source code
and template source are optional but allow error reporting
to work correctly.

handling for the given expression.
usage is like:  ${data | encoding('utf-8', errors='strict')}

implemented "args" for <%page> tag.  still has a default
"**_extra_pageargs" catchall for now...

- more docs

added filename-relative lookup to TemplateLookup

more pythonlike about scope:  variable assignment now follows python conventions (i.e., you lose access to the enclosing scope version when you assign locally)