missing imports
tidying up the state attrs in _ctx

- _penstyle now collects the line-drawing params
- _typestyle accumulates font() and align() settings
separated clip() and mask()

- it was awkward to have a trailing kwarg after a rect() or image() as
the stencil arg
text() can now be used in a `with bezier()` block

- it appends its path segments at the coords defined in the text()
call.