Fix various typos

Found via `codespell -q 3 -S ./ltmain.sh,./scripts/libtool.m4 -L ake,ans,ba,bloc,crashers,doed,inout,lengthh,maked,paeth,parm,parms,redy,unx`

contrib/libtests/timepng.c

@@ -527,7 +527,7 @@ int main(int argc, char **argv)
       }
    }
 
-   else if (nfiles == 0) /* Read from stdin withoout --dissemble */
+   else if (nfiles == 0) /* Read from stdin without --dissemble */
    {
       char filename[FILENAME_MAX+1];