Better error messages for misspelled keywords and similar characters

[Felienne]

Some old issues (like #268 and #1100 and #1116) refer to the more generic idea of fuzzy parsing: parsing less precise.

We now handle similar issues with specific error productions (like error_nq) but maybe we can solve this in a better way? The current approach does not handle keywords in the middle of lines, and I am not sure it would be feasible to make rules for that.

I see a few directions to explore:

• Explore the current strategy of error productions
• Fuzzy parsing: https://hackage.haskell.org/package/fuzzy-parse
• Symbol based program repair, not to repair but to give the right error message

[Felienne]

Moving this to Current since @akseron will pick this!