parse.py: Fix crash with non-control tags
compile.py: Compile jade comments to Jinja2 comments
parse.py: Clean up Parser.tag a bit
Add support for :filter block (compiles to Jinja2 filter block)
compile.py: Escape attribute values
compile.py: Add docstrings
parse.py: Parser.after_attr_key should drop the advanced rune
utils.py: Document repr_calling
Report line & column number in errors