Add RealTimeTrains API

[daveh6475]

Is there a simple way I can switch to using the RTT API rather than the National Rail one? Happy to mess around with the code a bit but don't want to mess the whole thing up for me!

[metacurb]

I think that there are other projects that use RTT, and this is a fork of those. For example, check out https://github.com/ghostseven/UK-Train-Departure-Display which uses the RTT!

[chrisys]

This one was forked when everyone was using Transport API (until they imposed usage limits), we went with National Rail as I think it was the best option at the time.

Are there any big benefits to using RTT instead (outside of implementation practicality)? I'm not against moving over (or providing a choice for everyone) if the benefits outweigh the effort.