include: Fixed some old Doxygen markup to be Markdown instead.

include/SDL3/SDL_iostream.h

@@ -73,16 +73,16 @@ typedef struct SDL_IOStreamInterface
     Sint64 (SDLCALL *size)(void *userdata);
 
     /**
-     *  Seek to \c offset relative to \c whence, one of stdio's whence values:
+     *  Seek to `offset` relative to `whence`, one of stdio's whence values:
      *  SDL_IO_SEEK_SET, SDL_IO_SEEK_CUR, SDL_IO_SEEK_END
      *
      *  \return the final offset in the data stream, or -1 on error.
      */
     Sint64 (SDLCALL *seek)(void *userdata, Sint64 offset, int whence);
 
     /**
-     *  Read up to \c size bytes from the data stream to the area pointed
-     *  at by \c ptr.
+     *  Read up to `size` bytes from the data stream to the area pointed
+     *  at by `ptr`.
      *
      *  On an incomplete read, you should set `*status` to a value from the
      *  SDL_IOStatus enum. You do not have to explicitly set this on
@@ -93,7 +93,7 @@ typedef struct SDL_IOStreamInterface
     size_t (SDLCALL *read)(void *userdata, void *ptr, size_t size, SDL_IOStatus *status);
 
     /**
-     *  Write exactly \c size bytes from the area pointed at by \c ptr
+     *  Write exactly `size` bytes from the area pointed at by `ptr`
      *  to data stream.
      *
      *  On an incomplete write, you should set `*status` to a value from the

include/SDL3/SDL_main.h

@@ -140,14 +140,15 @@
  *
  *  The application's main() function must be called with C linkage,
  *  and should be declared like this:
- *  \code
+ *
+ *  ```c
  *  #ifdef __cplusplus
  *  extern "C"
  *  #endif
  *  int main(int argc, char *argv[])
  *  {
  *  }
- *  \endcode
+ *  ```
  */
 
 #if defined(SDL_MAIN_NEEDED) || defined(SDL_MAIN_AVAILABLE) || defined(SDL_MAIN_USE_CALLBACKS)

include/SDL3/SDL_sensor.h

@@ -79,7 +79,8 @@ typedef Uint32 SDL_SensorID;
  *
  * Additional sensors may be available, using platform dependent semantics.
  *
- * Hare are the additional Android sensors:
+ * Here are the additional Android sensors:
+ *
  * https://developer.android.com/reference/android/hardware/SensorEvent.html#values
  *
  * Accelerometer sensor notes:

include/SDL3/SDL_test_common.h

@@ -27,7 +27,7 @@
  *  This code is a part of the SDL test library, not the main SDL library.
  */
 
-/* Ported from original test\common.h file. */
+/* Ported from original test/common.h file. */
 
 #ifndef SDL_test_common_h_
 #define SDL_test_common_h_