Move opusfile.h up a level.

This matches the convention used by opus itself, where
headers are included without a prefix, and the build
must do -I/path/to/opus to find the appropriate versions.

examples/opusfile_example.c

@@ -11,7 +11,7 @@
 # include <io.h>
 # include <fcntl.h>
 #endif
-#include <opus/opusfile.h>
+#include <opusfile.h>
 
 int main(int _argc,const char **_argv){
   OggOpusFile *of;

examples/seeking_example.c

@@ -12,7 +12,7 @@
 # include <io.h>
 # include <fcntl.h>
 #endif
-#include <opus/opusfile.h>
+#include <opusfile.h>
 
 /*Use shorts, they're smaller.*/
 #define OP_FIXED_POINT (1)

src/internal.h

@@ -18,7 +18,7 @@
 # endif
 
 # include <stdlib.h>
-# include <opus/opusfile.h>
+# include <opusfile.h>
 
 typedef struct OggOpusLink OggOpusLink;
 # if defined(OP_FIXED_POINT)

src/opusfile.c

@@ -22,7 +22,7 @@
 #include <string.h>
 #include <math.h>
 
-#include "opus/opusfile.h"
+#include "opusfile.h"
 
 /*This implementation is largely based off of libvorbisfile.
   All of the Ogg bits work roughly the same, though I have made some