Add ONNXRuntime python inference.

[itsnine]

@zhiqwang hi, I'm already done with this feature, could you check it? Temporary I did onnxruntime-python folder, but you could restructure folders as you want.
Let me know if you have any issues.
Resolve #177

[codecov]

Codecov Report

Merging #178 (c12b3db) into master (ed4c4eb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #178   +/-   ##
=======================================
  Coverage   96.16%   96.16%           
=======================================
  Files          10       10           
  Lines         600      600           
=======================================
  Hits          577      577           
  Misses         23       23           

Flag	Coverage Δ
unittests	96.16% <ø> (ø)

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[zhiqwang]

Thanks @itsnine , The overall looks very great to me. It is just additionally recommended to use the following process for committing PRs to keep the git history clean. I will cherry-pick directly your commits cd58b9b, db80c73 and related to merge this PR.

git remote add upstream https://github.com/zhiqwang/yolov5-rt-stack.git
git fetch upstream
git checkout -b feature  # <----- replace 'feature' with local branch name
git rebase upstream/master
git push -u origin -f

And I should add this tip to the CONTRIBUTING soon.

[zhiqwang]

Hi @itsnine , I'm merging this PR, let's refactor the restructure in #176 .