Flip options for sprues (#251) (#277)

* Flipping works, now just need new argument

* Finishing up

* New test data

samples/sprues/my_sprues/weird_sprue.yml

@@ -1,6 +1,6 @@
 ---
 sheet_width: 5in
-sheet_height: 4.5in
+sheet_height: 6.5in
 card_width: 2in
 card_height: 2in
 position_reference: :center
@@ -12,6 +12,10 @@ cards:
   rotate: 3.14159
 - x: 1.1in
   y: 3.1in
+  flip_horizontal: true
 - x: 3.1in
   y: 3.1in
-  rotate: 2 # 2 radians?? ew.
+  rotate: 2 # 2 radians?? ew. (this exists to annoy anyone who digs this deep)
+- x: 1.1in
+  y: 5.1in
+  flip_vertical: true