Implement set repr

[xarus01]

Fix#85

[codecov-io]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.85%. Comparing base (33327c5) to head (12fe2c0).

Files with missing lines	Patch %	Lines
py/set.go	85.71%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@ 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 

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[corona10]

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

Thank you :0

[corona10]

LGTM