AttributeDict could not pickle

[Ledenel]

According to python pickle, object containing pickable object (Including AttributeDict) should pickle.

But AttributeDict implements __reduce__ which override the origin pickle process, and even call __reduce__ on __dict__ doesn't actually pickle a dict. Instead, it will throw TypeError: can't pickle dict objects even the __dict__ itself is pickable.

[codecov]

Codecov Report

Merging #8 into master will increase coverage by 0.51%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   89.03%   89.54%   +0.51%     
==========================================
  Files           3        3              
  Lines         155      153       -2     
==========================================
- Hits          138      137       -1     
+ Misses         17       16       -1     

Impacted Files	Coverage Δ
attributedict/collections.py	87.87% <ø> (+0.56%)	⬆️

---

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 26c69ad...fbb2c26. Read the comment docs.

[Ledenel]

Add unittest to reproduce and simply remove reduce to fix it.