Allow for custom host

[Ryuno-Ki]

Allow to define a host (according to Express.js documentation this would be the second argument to

yari/server/index.js

Line 240 in ae2020b

app.listen(PORT, () => {

) so a local instance could be checked from other devices on the same network, by passing in 0.0.0.0.
Useful when testing with a mobile (resp. the screenreader there, in my case).

[peterbe]

Doesn't Expression already listen to some default environment variables? Can you find out?

[Ryuno-Ki]

It does. NODE_ENV for production environments and DEBUG for trouble shooting.

Searching through the codebase, I can't spot further environment variables (except in testing or benchmarking scenarios).