https://github.com/navit-gps/navit/pull/877

This pull request adds the possibility to globally set a default for icon size of a layout.
You can now give "icon_h" and "icon_w" properties in "layout" tag. This causes navit to not use the real size of an icon but to scale it to have the requested size. Guessing prescaled icons (the name_w_h.png's of course works. Default size of 22x22px which is the default size hint on most of the svg's is used. This fixes #819.

This pull request adds the property "underground_alpha" to the "graphics" tag giving the alpha value to use as transparency if ways are flagged with AF_UNDERGROUND. This effectively renders tunnels in transparent.

This pull request adds a "oneway" tag to itemgras in layouts. Together with the enhancements of the "arrows" itemgra used for drawing the route graph one can print nice arrows on oneway roads.

* fix:core:refactor polygon clipping

This commit extracts the polygon clipping into its own function to be
re used for polygon with holes clipping.

* fix:core:Clip polygons with holes prior drawing.

While this helps drawing for limited graphics like SDL or WindowsCE,
it will slightly slow down on graphics that do clipping themselves like
qt5. As this is done for polygons already, we do this for polygons with
holes as well.

We're getting close. Finally processed map of Oberbayern, Germany
without any issues. Renders nicely on Qt5. Nedds still some hacks in
maptool as I did not understan everything properly. Parts of maptool are
rather hacky, aren't they?