migrate to midje for core.models.history and some kondo/kibit cleaning

[gkspranger]

• project.clj
  • added kibit to plugins
• src/yetibot/core/models/history.clj
  • some kondo cleaning of unused refs and "vars"
  • small change to (not=) vs (not (=))
• test/README.md
  • update on how to use kibit locally
• test/yetibot/core/test/models/history.clj
  • migrate to midje
  • i think this is THE LAST of real use of clojure.test in core 🥳 🎈 👯 🕺
  • ^^ minus one use of (function?) on a return type

[codecov[bot]]

Codecov Report

Merging #192 (7950d29) into master (0603970) will increase coverage by 0.01%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #192      +/-   ##
==========================================
+ Coverage   54.33%   54.34%   +0.01%     
==========================================
  Files          94       94              
  Lines        4130     4131       +1     
  Branches      210      209       -1     
==========================================
+ Hits         2244     2245       +1     
- Misses       1676     1677       +1     
+ Partials      210      209       -1     

Impacted Files	Coverage Δ
src/yetibot/core/models/history.clj	83.87% <66.66%> (+0.17%)	:arrow_up:

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