Backports for 0.6

[vchuravy]

• Test on 1.6, 1.7, and 1.8
• Update CI.yml
• Type rule for pointer_from_objref (Type rule for pointer_from_objref #83)
• Mark print as inactive (Mark print as inactive #85)
• add release to CI

[codecov-commenter]

Codecov Report

Merging #89 (f8fbb01) into release-0.6 (bb95bc4) will increase coverage by 0.23%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           release-0.6      #89      +/-   ##
===============================================
+ Coverage        74.82%   75.05%   +0.23%     
===============================================
  Files               12       12              
  Lines             1287     1291       +4     
===============================================
+ Hits               963      969       +6     
+ Misses             324      322       -2     

Impacted Files	Coverage Δ
src/compiler.jl	84.01% <100.00%> (+0.44%)	⬆️
src/typetree.jl	83.33% <0.00%> (+0.20%)	⬆️

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