Elevation

- Import elevation from osm node tag 'ele';
- Optional elevation in JSON and GPX formats;
- Basic support for elevation cucumber tests.

The elevation is stored as an int.
Using a smaller structure would lead to misalignement or no gain.

The routing algorithm is unchanged.

The elevation feature must be enabled at compile time with:
cmake option -DOSRM_HAS_ELEVATION:BOOL=ON and each tool must be passed
the '-e 1' parameter to activate it. Finally, the viaroute request must
include the 'elevation=true' parameter.

The elevation is read as meters from the osm data.
Since we must store it as an int, there is 1cm precision.
It is then exported as 10^4 meters in JSON.
Generate OSRM_config.h in source include directory.
Remove unused test method