Speed up OSMData -> MapData

[blegat]

Adding a @time at this line:

OpenStreetMapX.jl/src/parseMap.jl

Line 102 in 7a06505

res = MapData(mapdata, road_levels, only_intersections; trim_to_connected_graph=trim_to_connected_graph)

Before this PR, I get:

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.097901 seconds (222.99 k allocations: 50.380 MiB)

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.086140 seconds (222.99 k allocations: 50.380 MiB)

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.150200 seconds (222.99 k allocations: 50.380 MiB, 40.81% gc time)

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.090045 seconds (222.99 k allocations: 50.380 MiB)

After this PR, I get

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.026511 seconds (29.02 k allocations: 8.461 MiB)

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.027412 seconds (29.02 k allocations: 8.461 MiB)

julia> get_map_data("/home/blegat/Downloads/andorra-latest.osm", use_cache=false);
  0.027245 seconds (29.02 k allocations: 8.461 MiB)

[pszufe]

wow! this looks impressive in terms of performance.
Perhaps here and there still is space for improvement by changing Strings to Symbols but this is a minor difference compared to this change