Use tracing for logging

[gakonst]

Is your feature request related to a problem? Please describe. Currently the library offers no logging.

Describe the solution you'd like

Tracing provides great logging support with various levels of verbosity along with contexts, instead of using println calls. Example of past integration:

https://github.com/celo-org/snark-setup/pull/44 https://github.com/celo-org/snark-setup/pull/43

[hariamoor-zz]

Hi: If this issue is being considered, I'd be happy to get started by providing a contribution, e.g., with the given library. Please let me know if this is necessary.

[gakonst]

Go for it!