Add cap and join style to bezier path.

[fdb]

The BezierPath class should support cap style (butt, round or square) and join style (miter, round, bevel).

NSBezierPath implements cap style and join style, so supporting this is a matter of making the attributes available in the appropriate places:

• The cap style and join style should be context state variables, available under capstyle() and joinstyle()
• The BezierPath should inherit these state variables when creating a new bezier path.
• The BezierPath should have getters / setters for cap style and join style.
• The BezierPath constructor should accept capstyle and joinstyle arguments.

[dimitre]

joinstyle() is working but Path.joinstyle and Path.capstyle are not.
here is the minimum code to reproduce the issue

nofill()
stroke(0)
strokewidth(10)
beginpath(40, 40)
lineto(140, 140)
lineto(280, 140)
path = endpath(draw=False)
#path.capstyle = ROUND
path.joinstyle = ROUND

#joinstyle(ROUND)
drawpath(path)