Doc test readme

[hepengfe]

This PR fixes #829.

Description of changes

• change TerminalReader to StringReader
• fixed the issue Doctest for README #829 (comment)
• add package mkcodes that convert markdown code into python script
• generate python script based on latest README, test it and remove it after testing

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Test Conducted

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[codecov]

Codecov Report

Merging #830 (ed96565) into master (ac34f10) will not change coverage.
The diff coverage is n/a.

❗ Current head ed96565 differs from pull request most recent head f9e7bed. Consider uploading reports for the commit f9e7bed to get more accurate results

@@           Coverage Diff           @@
##           master     #830   +/-   ##
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  Coverage   80.50%   80.50%           
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  Files         252      252           
  Lines       19363    19363           
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  Hits        15588    15588           
  Misses       3775     3775           

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Need to update the test-markdown conversion

[hunterhector]

I find markdown autodoc to be a better alternative. Instead of extracting code from a markdown (which is a bit hacky), we just need to add a tested piece of code into the README.