Support rust logging

[austinabell]

Is your feature request related to a problem? Please describe.
Rust logging through the https://docs.rs/log/0.4.14/log/ interface allows the user to have control over how the logs are output, instead of forcing printing to std out. This can be useful if someone wants to ignore logs from any/all modules, log asynchronously, have variable log levels, or even change where the logs are output.

Describe the solution you'd like

println! usages switched to log equivalents.

[gakonst]

We already do this with tracing! Each request made to the node is logged this way: https://github.com/gakonst/ethers-rs/blob/master/ethers-providers/src/provider.rs#L117-L127

[austinabell]

We already do this with tracing! Each request made to the node is logged this way: https://github.com/gakonst/ethers-rs/blob/master/ethers-providers/src/provider.rs#L117-L127

Ah okay my bad I didn't see, the files I looked in when checking were using println iirc. I'll have another look to see, maybe I'll make a pass through to swap those?

[gakonst]

That sounds good to me! Thank you.