WRaster: add functions to save image on disk

This patch adds the RSaveTitledImage() function to the WRaster lib
to be able to save file on disk either as a PNG or a JPEG file.
Those two formats depends on optional external libs.
The function can take an optional title/comment which will
be save inside the file.

The WRaster lib and header versions are bumped.

wrlib/Makefile.am

@@ -55,10 +55,12 @@ endif
 
 if USE_JPEG
 libwraster_la_SOURCES += load_jpeg.c
+libwraster_la_SOURCES += save_jpeg.c
 endif
 
 if USE_PNG
 libwraster_la_SOURCES += load_png.c
+libwraster_la_SOURCES += save_png.c
 endif
 
 if USE_TIFF