Reorganize tags and cleanup

src/tags.rs

@@ -111,12 +111,12 @@ pub enum Tag(u16) unknown("A private or extension tag") {
     Threshholding = 263, // TODO add support
     XResolution = 282,
     YResolution = 283,
-    // JPEG
     TileWidth = 322,
     TileLength = 323,
     TileOffsets = 324,
     TileByteCounts = 325,
     SampleFormat = 339,
+    // JPEG
     JPEGTables = 347,
     // Advanced tags
     Predictor = 317,