Implement set repr

[xarus01]

Fix #85

[codecov-io]

Codecov Report

Merging #117 into master will increase coverage by 0.01%.
The diff coverage is 89.47%.

@@            Coverage Diff             @@
##           master     #117      +/-   ##
==========================================
+ Coverage   72.84%   72.85%   +0.01%     
==========================================
  Files          60       60              
  Lines       11935    11949      +14     
==========================================
+ Hits         8694     8706      +12     
- Misses       2708     2709       +1     
- Partials      533      534       +1

Impacted Files	Coverage Δ
py/range_repr110.go	70% <ø> (ø)	⬆️
builtin/builtin.go	80.21% <100%> (ø)	⬆️
py/range.go	86.66% <100%> (ø)	⬆️
py/set.go	76.19% <85.71%> (+1.19%)	⬆️

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[corona10]

1. Please resolve the conflict
2. There are some codes that are not related to Implement set repr #85, please revert them.

Thank you :0

[corona10]

LGTM