cosmetics & warnings

- remove some unused functions
- move global arrays from data to read only section
- explicitly cast malloc returns; not specifically necessary, but helps
  show intent
- miscellaneous formatting

Change-Id: Ib15fe5b37fe6c29c369ad928bdc3a7290cd13c84

examples/cwebp.c

@@ -443,7 +443,7 @@ static int ReadPNG(FILE* in_file, WebPPicture* const pic, int keep_alpha) {
 typedef enum {
   PNG = 0,
   JPEG,
-  UNSUPPORTED,
+  UNSUPPORTED
 } InputFileFormat;
 
 static InputFileFormat GetImageType(FILE* in_file) {