Make MTA (NY) GTFS data work correctly

[moshobo]

Fix any outstanding error cases in order to make MTA data work with Transit Simulator

[moshobo]

I've looked into this a bit, and it seems that some shapes returned by the GTFS feed from the MTA return nan. This is causing gtfs_kit's append_dist_to_stop_times() function to error out.

I've created an issue in gtfs_kit to discuss what's going on here; whether it's a gfts_kit issue or something that the MTA is screwing up (who would be surprised). I will update this issue when there are further developments.

If you create a workaround to skip these nan values, the rest of the code seems to work just fine. I was able to create an exported map for all subway lines.