Feature/api improve

[JayDwee]

Summary

close #400

Checklist

• [x] This PR fixes an issue.
• [ ] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

• [x] Have you tested the changes? (pytest & dpytest)
• [x] Have you followed PEP-8 for naming and styling?
• [ ] Has your code been properly documented with RestructuredText docstrings?
• [ ] Have you added your changes to CHANGELOG.md under the [Unreleased] heading?
• [ ] If your code added new bot commands, have you updated documentation.json?

• [x] All of this code is your own, or follows the author repo's licence.

[codecov[bot]]

Codecov Report

Merging #413 (c2fb268) into master (d61d49f) will increase coverage by 0.00%. The diff coverage is 97.77%.

@@           Coverage Diff           @@
##           master     #413   +/-   ##
=======================================
  Coverage   87.40%   87.40%           
=======================================
  Files         123      123           
  Lines        8961     8981   +20     
=======================================
+ Hits         7832     7850   +18     
- Misses       1129     1131    +2     

Flag	Coverage Δ
unittests	87.40% <97.77%> (+<0.01%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
koala/utils.py	94.52% <83.33%> (-2.26%)	:arrow_down:
koala/cogs/react_for_role/api.py	91.66% <100.00%> (ø)
koala/rest/api.py	93.15% <100.00%> (+0.50%)	:arrow_up:
koala/rest/dto.py	100.00% <100.00%> (ø)
tests/cogs/base/test_api.py	100.00% <100.00%> (ø)
tests/cogs/verification/test_api.py	81.44% <100.00%> (ø)