Unit conversion on save_pdf, and arbitrary paper sizes

Closes #21 and #20

spec/data/samples/saves.rb.txt

@@ -542,6 +542,10 @@ cairo: set_source([MockDouble, -37, -37])
 cairo: paint([])
 cairo: set_source([MockDouble, 1650, 75])
 cairo: paint([])
+cairo: set_source([MockDouble, 75, 75])
+cairo: paint([])
+cairo: set_source([MockDouble, 175, 75])
+cairo: paint([])
 surface: write_to_png(["_output/saves_notrim_01.png"])
 cairo: set_source([MockDouble, -37, -37])
 cairo: paint([])

spec/input_helpers_spec.rb

@@ -176,6 +176,13 @@ describe Squib::InputHelpers do
       expect(opts).to eq({:x => [236.2204722] }) #assume 300dpi default
     end
 
+    it 'handles non-expading singletons' do
+      args = {margin: '1in', trim: '1in', gap: '1in'}
+      needed_params = [:margin, :trim, :gap]
+      opts = @deck.send(:convert_units, args, needed_params)
+      expect(opts).to eq({margin: 300, trim: 300, gap: 300}) #assume 300dpi default
+    end
+
   end
 
   context '#rowify' do