define new style settings text.aa, lineaa and fill.aa each based on

define new style settings text.aa, lineaa and fill.aa each based on
the top level "aa" style.  Each text style depends on text.aa, each
line style depends on lineaa.

add _line_style() to populate a hash similar in concept to that used
by by _text_style(), so we can easily support pens and thick lines
from future Imager