docs: document effect cleanups & comment why ES5-style prototypes are used

[jviide]

This pull request adds minor bits of documentation.

• Add a comment to the source code why ES5-style prototypes are used instead of ES6-style classes.
• Add documentation mentioning effect cleanups in README.md.
• Fix README.md's section order that was not in sync with the table of contents in the beginning of README.md.

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Latest commit: 590a466

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[marvinhagemeister]

Good idea!