Added line cap and join settings for rect and curve

More forthcoming - these are proof-of-concept

spec/args/draw_spec.rb

@@ -0,0 +1,27 @@
+require 'spec_helper'
+require 'squib/args/box'
+
+describe Squib::Args::Draw do
+  subject(:draw) { Squib::Args::Draw.new }
+
+  context 'unit conversion' do
+
+    it 'converts units on stroke width' do
+      args = {stroke_width: '2in'}
+      draw.load!(args, expand_by: 2)
+      expect(draw).to have_attributes(stroke_width: [600, 600])
+    end
+
+  end
+
+  context 'validation' 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])
+    end
+
+  end
+
+end