[mkgmap-dev] [PATCH] support of DEM subfile for Displayer

This patch enables the display tool to read the known parts of DEM subfiles. Please refer to http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/DEM_Subfile_Format for a description. Notes: - Using the discovered parts it is possible to read the coordinates of the covered areas, their minimum and maximum heights and the data which builds the real elevation model. - The encryption of this data is still unknown. IMHO it is normalized (using the difference between minimum and maximum height and perhaps an additional field) and compressed. But I'm not an expert on data encrytion ;-)