Generate an R5 network.dat

[stupidpupil]

https://ipeagit.github.io/r5r/index.html

[stupidpupil]

https://github.com/ipeaGIT/r5r/issues/187

[stupidpupil]

This is going to ultimately require:

• Explicitly separating OTP and R5 configuration files
• Relabelling the project
• Explaining how to get started with r5r
• Explaining when you'd want to use OTP vs R5
• Documenting known issues with each (e.g. R5's lack of left-hand-drive support)

[stupidpupil]

Simply generating an R5 network.dat is now merged (https://github.com/stupidpupil/wales_ish_otp_graph/pull/19), but many of the above items remain unresolved.

[stupidpupil]

Example of use: https://gist.github.com/stupidpupil/cb60575c5add1b28f0146ff2802424c1

[stupidpupil]

The situation with competing build-config.json (between R5 and OTP) is very messy!

[stupidpupil]

Probably need to configure R5 driving speeds.

Need to document R5 limitations, including lack of proper left-hand drive.

[stupidpupil]

Need to look at r5r's support for incorporating elevation into weights/speed

[stupidpupil]

Terrain 50 DEM now used for r5r if present.

EDIT: Reverted, because I didn't understand how r5r tries to use DEM TIFFs at runtime

[stupidpupil]

Although I think I've probably misunderstood how r5r uses elevation data - I suspect it needs to be present at runtime, not at network generation time.

[stupidpupil]

Need to configure driving speeds, as well as document driving limitations per #24