added random_queryset into QuerySet manager

[agusmakmun]

fixed #13

[codecov]

Codecov Report

Merging #14 (b56d7a8) into master (76b422a) will decrease coverage by 0.54%.
The diff coverage is 50.00%.

❗ Current head b56d7a8 differs from pull request most recent head a7689bb. Consider uploading reports for the commit a7689bb to get more accurate results

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
- Coverage   97.27%   96.73%   -0.55%     
==========================================
  Files          13       13              
  Lines         367      367              
==========================================
- Hits          357      355       -2     
- Misses         10       12       +2     

Impacted Files	Coverage Δ
reobject/query/queryset.py	96.46% <50.00%> (-1.74%)	⬇️
reobject/models/manager.py	93.93% <0.00%> (-0.10%)	⬇️
reobject/models/model.py	100.00% <0.00%> (ø)

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