Update log to use kv_unstable_std instead of std

[KodrAus]

Part of rust-lang/log#437

The log crate has an unstable structured logging API under the kv_unstable feature. In previous releases, if you specified both the kv_unstable and std features of log like so:

log = { features = ["std", "kv_unstable"]}

you'd get support for standard library types in log's structured logging API.

Going forward, this functionality is now gated under kv_unstable_std:

log = { features = ["kv_unstable_std"]}

This change was made because we need to enable features in optional dependencies when both the std and kv_unstable features are enabled, which isn't currently supported by Cargo.

This PR updates this library to follow the new approach. It can be merged at any time and is currently non-blocking, but on 2020-01-18 the version of log requiring kv_unstable_std instead of kv_unstable and std will be published.

Thanks for trying out log's structured logging API and sorry for any disruption! 🙇

[jbr]

i believe this closes #787

[KodrAus]

It should, yes 👍

It was unfortunate to have to break but I’m trying to avoid any more until we can stabilize the API proper.

[pepoviola]

Hi @KodrAus, thanks for the pr! I just resolve the conflict. ping @yoshuawuyts I think is ready to merge :)
Thx!

[yoshuawuyts]

Fixed in v0.15.1. Release notes: https://github.com/http-rs/tide/releases/tag/v0.15.1