Add logging level

[mojoX911]

Update println!s to log::trace. Fixes #20

log seems like the lightest of all the crates available.

Changed printlns to log::trace mostly. As it seems most errors and messages are to be displayed by default.

We might decide to add other log levels later from different internal parts.

Added target in logging as the module name generating the message.

Kept few printlns intact as they are used for user level communication.

[codecov-commenter]

Codecov Report

Merging #22 (a5aea8c) into master (9ddd6db) will decrease coverage by 0.83%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master      #22      +/-   ##
==========================================
- Coverage   84.22%   83.38%   -0.84%     
==========================================
  Files           8        8              
  Lines        2504     2504              
==========================================
- Hits         2109     2088      -21     
- Misses        395      416      +21     

Impacted Files	Coverage Δ
src/main.rs	48.07% <0.00%> (ø)
src/offerbook_sync.rs	83.09% <33.33%> (ø)
src/wallet_sync.rs	81.53% <50.00%> (-0.18%)	⬇️
src/taker_protocol.rs	95.02% <91.66%> (-1.09%)	⬇️
src/maker_protocol.rs	85.67% <100.00%> (-0.82%)	⬇️
src/messages.rs	86.90% <0.00%> (-11.91%)	⬇️

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[chris-belcher]

Thanks for the PR. I'll try it out soon and then merge.