Two dimensional geo-coordinates

There often only two dimensional coordinates for geo mappings, e.g. longitude and latitude without altitude/height.

e.g. EPSG-Code 4326 serves the horizontal component of WGS 84

Second EPSG-Code (extraHeight) should be optional: see Ticket #49 (closed)

coord Attribut in Type tPlacedElement should have

'''<maxLength value="3"/> instead of <length value="3"/>.

Maybe additional <minLength value="2"/> would help either.

Current code without altitude information is wrong:

<rail:geoCoord coord="51.040278 13.731389 0"/>