Use diffs on comments to extract human content from bot modifications

[gentlementlegen]

          Reliably depends mostly on GitHub API I suppose, sometimes I must say it looks weird because the "diff" is just the comment you posted not a diff formatted content. Making a separate spec to explore this.

Originally posted by @gentlementlegen in #188 (comment)

We should try to use diff to understand the edits on bodies and comments and avoid crediting the bot for its changes, only the human made edits.

What should be done:

• diff the whole history on the bodies of issues to remove the bot content from evaluation
• likewise for comments
• likewise for review comments

A library that might help: https://www.npmjs.com/package/diff