Add dash option to drawing operations

Currently only impacts rect, but it will impact others with the new design shortly

spec/args/draw_spec.rb

@@ -19,7 +19,28 @@ describe Squib::Args::Draw do
     it 'converts to Cairo options' do
       args = {join: 'bevel', cap: 'round'}
       draw.load!(args)
-      expect(draw).to have_attributes(join: [Cairo::LINE_JOIN_BEVEL])
+      expect(draw).to have_attributes(
+        join: [Cairo::LINE_JOIN_BEVEL],
+        cap: [Cairo::LINE_CAP_ROUND]
+        )
+    end
+
+    it 'parses dash options' do
+      args = {dash: '3 4 5'}
+      draw.load!(args)
+      expect(draw).to have_attributes(dash: [[3, 4, 5]])
+    end
+
+    it 'parses more complex dash options' do
+      args = {dash: '30.5,  90,  5'}
+      draw.load!(args)
+      expect(draw).to have_attributes(dash: [[30.5, 90, 5]])
+    end
+
+    it 'does unit conversion on dash options' do
+      args = {dash: '3in  4in 5in'}
+      draw.load!(args)
+      expect(draw).to have_attributes(dash: [[900, 1200, 1500]])
     end
 
   end