milestone..
add Interface SCOperable.
add new Operater `shape'
Add new Operater `Painter', copy from sc-shape, and take some substituting.
implement SCPainter,
add new operator `SCArrow'.
Color Picker Widget of Operators.
implement SCWidthSetter.
add SCLine.
use color-spec instead of GdkRGBA.
implement SCArrow.
Fix.
Fix.
almost play well.
move operables' register to sc-operators .
add function of saving picture .
add sc_canvas_set_appwin().
complete sc-arrow .
fix force type casting.
tune width of decorator(selected rectangle).