Negative Keyword Filtering

[grantmulholland]

Is your feature request related to a problem? Please describe.
Some recipes I have saved (for others) contain items that I am allergic to, I want to filter them out.
I think that using keywords would do a good enough job, just attach something like "peanuts" to a recipe, and filter it out.

Describe the solution you'd like
Having the ability to set a filter to exclude a keyword would do great.
There's an existing "venn diagram" button that I expected to do the trick, but either it's broken, or I misunderstand its function.

[christianlupus]

We should check if the schema.org standard allows for explicit allergenes.