add plot_logs tool

[xiexinch]

Support plot logs by matplotlib.

[codecov]

Codecov Report

Merging #426 (cbd75cf) into master (7e1b24d) will not change coverage.
The diff coverage is n/a.

❗ Current head cbd75cf differs from pull request most recent head 29d2c0a. Consider uploading reports for the commit 29d2c0a to get more accurate results

@@           Coverage Diff           @@
##           master     #426   +/-   ##
=======================================
  Coverage   86.44%   86.44%           
=======================================
  Files          97       97           
  Lines        4958     4958           
  Branches      805      805           
=======================================
  Hits         4286     4286           
  Misses        517      517           
  Partials      155      155           

Flag	Coverage Δ
unittests	86.44% <ø> (ø)

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[xvjiarui]

We may also update the doc.