Minor documentation fixes and improvements.

include/freetype/freetype.h

@@ -2099,7 +2099,8 @@ FT_BEGIN_HEADER
    *     The size in bytes of the file in memory.
    *
    *   pathname ::
-   *     A pointer to an 8-bit file pathname.  The pointer is not owned by
+   *     A pointer to an 8-bit file pathname, which must be a C~string (i.e.,
+   *     no NULL bytes except at the very end).  The pointer is not owned by
    *     FreeType.
    *
    *   stream ::
@@ -2186,9 +2187,12 @@ FT_BEGIN_HEADER
    *   FreeType error code.  0~means success.
    *
    * @note:
-   *   The `pathname` string should be reconizable as such by a standard
-   *   `fopen()` call on your system.  If that is not sufficient to address
-   *   all file name possiblities, you can use @FT_Open_Face.
+   *   The `pathname` string should be recognizable as such by a standard
+   *   `fopen` call on your system; in particular, this means that `pathname`
+   *   must not contain NULL bytes.  If that is not sufficient to address all
+   *   file name possibilities (for example, to handle wide character file
+   *   names on Windows in UTF-16 encoding) you might use @FT_Open_Face to
+   *   pass a memory array or a stream object instead.
    *
    *   Use @FT_Done_Face to destroy the created @FT_Face object (along with
    *   its slot and sizes).