implement circle arc feature, no tests

lib/squib/args/coords.rb

@@ -16,7 +16,9 @@ module Squib
           cx2: 0 , cy2: 0,
           inner_radius: 50, outer_radius: 100,
           radius: 100,
-          n: 5, }
+          n: 5,
+          arc_start: 0, arc_end: 2 * Math::PI, arc_ccw: false, arc_close: false,
+       }
       end
 
       def self.expanding_parameters

lib/squib/graphics/cairo_context_wrapper.rb

@@ -25,7 +25,7 @@ module Squib
         :operator=, :show_page, :clip, :transform, :mask, :create_pango_layout,
         :antialias=, :curve_to, :matrix, :matrix=, :identity_matrix, :pango_layout_path,
         :stroke_preserve, :target, :new_path, :fill_preserve, :close_path,
-        :set_line_join, :set_line_cap, :set_dash
+        :set_line_join, :set_line_cap, :set_dash, :arc, :arc_negative
 
       # :nodoc:
       # @api private

lib/squib/graphics/shapes.rb

@@ -18,8 +18,15 @@ module Squib
     def circle(box, draw)
       x, y, r = box.x, box.y, box.radius
       use_cairo do |cc|
-        cc.move_to(x + r, y)
-        cc.circle(x, y, r)
+        # cc.move_to(x + r, y)
+        if box.arc_ccw
+          cc.arc_negative(x, y, r, box.arc_start, box.arc_end)
+        else
+          cc.arc(x, y, r, box.arc_start, box.arc_end)
+        end
+        if box.arc_close
+          cc.close_path();
+        end
         cc.fill_n_stroke(draw)
       end
     end