fix comments

handlers/blankpng.go

@@ -1,5 +1,7 @@
 package handlers
 
+// BlankPNG returns bytes of a blank PNG, for the request handlers to return
+// when an image tile is not available.
 func BlankPNG() []byte {
 	return []byte{
 		0x89, 0x50, 0x4e, 0x47, 0xd, 0xa, 0x1a, 0xa, 0x0, 0x0, 0x0, 0xd, 0x49,

handlers/handlers.go

@@ -157,7 +157,7 @@ func NewFromBaseDir(baseDir string) (*ServiceSet, error) {
 	return s, nil
 }
 
-// Len returns the number of tilesets in this ServiceSet
+// Size returns the number of tilesets in this ServiceSet
 func (s *ServiceSet) Size() int {
 	return len(s.tilesets)
 }