docs: Add IJON Documents

[potetisensei]

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#19

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PR Overview

This PR adds docs/ijon/algorithm_{ja,en}.md and docs/ijon/implementation_{ja,en}.md. Also, this PR formats some other documents and fixes trivial typos in them.

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• Performance
• Source Code Quality

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[ptr-yudai]

Reviewed. I fixed some expressions I couldn't get.
Put a link to IJON on README.md and README_ja.md if necessary.

[ptr-yudai]

Please provide an example of how to write annotations in a program and how to compile it.
You should put a link to ijon-cc in the "Usage on CLI" section at least.

[Fadis]

run tests

[ptr-yudai]

LGTM