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

* Flipping works, now just need new argument

* Finishing up

* New test data

docs/args/transform.rst

@@ -48,4 +48,4 @@ flip_horiztonal
 flip_vertical
   default: ``false``
 
-  Flip this image about its center verticall (i.e. top becomes bottom and vice versa).
+  Flip this image about its center vertical (i.e. top becomes bottom and vice versa).

docs/sprues.rst

@@ -156,6 +156,16 @@ rotate
 
   Rotate the card around its position_reference. Allows ``clockwise``, ``counterclockwise``, or ``turnaround``, or numerical angle.
 
+flip_vertical
+  Default: ``false``
+
+  Determine whether or not to flip the card vertically about the vertical line through the card's its position reference. Works most intuitively with ``position_reference: :center``
+
+flip_horizontal
+  Default: ``false``
+
+  Determine whether or not to flip the card vertically about the horizontal line through the card's its position reference. Works most intuitively with ``position_reference: :center``
+
 crop_line
 ^^^^^^^^^