new opfilter transfrom for whitelisting and blacklisting message ops

[jipperinbham]

fixes #342

• CHANGELOG.md updated
• README.md updated

[codecov]

Codecov Report

Merging #401 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #401      +/-   ##
==========================================
+ Coverage    84.2%   84.27%   +0.07%     
==========================================
  Files          60       61       +1     
  Lines        4115     4134      +19     
==========================================
+ Hits         3465     3484      +19     
  Misses        482      482              
  Partials      168      168

Impacted Files	Coverage Δ
function/opfilter/opfilter.go	100% <100%> (ø)

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