Implement tag based constraint definition

[adam-urbanczyk]

Will resolve #467 .

[codecov]

Codecov Report

Merging #514 (55d1f3c) into master (ec9cd46) will increase coverage by 0.37%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #514      +/-   ##
==========================================
+ Coverage   93.75%   94.13%   +0.37%     
==========================================
  Files          30       30              
  Lines        6007     6800     +793     
  Branches      637      765     +128     
==========================================
+ Hits         5632     6401     +769     
- Misses        237      254      +17     
- Partials      138      145       +7     

Impacted Files	Coverage Δ
cadquery/assembly.py	90.00% <100.00%> (+1.56%)	⬆️
cadquery/cq.py	88.67% <100.00%> (+0.22%)	⬆️
tests/test_assembly.py	100.00% <100.00%> (ø)
tests/test_cadquery.py	99.03% <100.00%> (+<0.01%)	⬆️
tests/test_cad_objects.py	98.23% <0.00%> (-0.77%)	⬇️
tests/test_selectors.py	100.00% <0.00%> (ø)
cadquery/selectors.py	99.38% <0.00%> (+0.28%)	⬆️
cadquery/occ_impl/shapes.py	92.94% <0.00%> (+1.69%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ec9cd46...20eb996. Read the comment docs.

[adam-urbanczyk]

I think this PR is ready for merging, could you take a look @jmwright ?

[adam-urbanczyk]

@marcus7070 you are probably also interested

[jmwright]

@adam-urbanczyk Looks good, thanks!