lavu/avstring: switch AV_ESCAPE_FLAGs to shift-based formatting

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/avstring.h

@@ -300,14 +300,14 @@ enum AVEscapeMode {
  * characters lists, except it is guaranteed to use the exact same list
  * of whitespace characters as the rest of libavutil.
  */
-#define AV_ESCAPE_FLAG_WHITESPACE 0x01
+#define AV_ESCAPE_FLAG_WHITESPACE (1 << 0)
 
 /**
  * Escape only specified special characters.
  * Without this flag, escape also any characters that may be considered
  * special by av_get_token(), such as the single quote.
  */
-#define AV_ESCAPE_FLAG_STRICT 0x02
+#define AV_ESCAPE_FLAG_STRICT (1 << 1)
 
 /**
  * Escape string in src, and put the escaped string in an allocated