Add missing "none" BlendMode;

api/init.lua

@@ -10664,6 +10664,10 @@ return {
             {
               name = "screen",
               description = "The opposite of multiply: the pixel colors are inverted, multiplied, and inverted again, producing a lightening effect."
+            },
+            {
+              name = "none",
+              description = "The incoming colors will replace the existing colors.  This is the same as using a blend mode of `nil`."
             }
           }
         },

api/lovr/graphics/BlendMode.lua

@@ -32,6 +32,13 @@ return {
         The opposite of multiply: the pixel colors are inverted, multiplied, and inverted again,
         producing a lightening effect.
       ]]
+    },
+    {
+      name = 'none',
+      description = [[
+        The incoming colors will replace the existing colors.  This is the same as using a blend
+        mode of `nil`.
+      ]]
     }
   },
   related = {