Tendermint config handle optional values + fix net::Address Display

[tzemanovic]

closes #906, #907

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #908 (22d82eb) into master (05da904) will increase coverage by 0.2%.
The diff coverage is 86.0%.

❗ Current head 22d82eb differs from pull request most recent head eacdc2a. Consider uploading reports for the commit eacdc2a to get more accurate results

@@           Coverage Diff            @@
##           master    #908     +/-   ##
========================================
+ Coverage    70.5%   70.7%   +0.2%     
========================================
  Files         203     203             
  Lines       16204   16228     +24     
========================================
+ Hits        11424   11477     +53     
+ Misses       4780    4751     -29     

Impacted Files	Coverage Δ
tendermint/tests/config.rs	96.1% <77.7%> (-1.2%)	⬇️
tendermint/src/config.rs	65.8% <84.3%> (+5.0%)	⬆️
tendermint/src/net.rs	90.8% <100.0%> (+8.3%)	⬆️
tendermint/src/timeout.rs	83.0% <100.0%> (+13.2%)	⬆️
tendermint/src/trust_threshold.rs	78.9% <0.0%> (-14.9%)	⬇️
tendermint/src/node.rs	65.9% <0.0%> (-0.3%)	⬇️
tendermint/src/hash.rs	36.4% <0.0%> (-0.2%)	⬇️
light-client/src/types.rs	30.6% <0.0%> (ø)
tendermint/src/abci/path.rs	0.0% <0.0%> (ø)
tendermint/src/signature.rs	56.4% <0.0%> (+1.4%)	⬆️
... and 3 more

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[thanethomson]

Thanks for this!

For some reason the doc test (which runs on Rust nightly) keeps failing here. I ran the doc tests locally on my machine for this PR, using nightly, and it compiles just fine, so I'm not sure what the problem is.