Recipe-scrapers

Adds support for:

- grouprecipes.com (873)
- norecipes.com (871)

And adds ingredient group functionality to:

- Add A Pinch
- Allt om Mat
- Alton Brown
- Amazing Ribs

... courtesy of pull request 874.

Thanks again, jknndy!

A smorgasbord of additional scrapers thanks to jknndy as is standard recently :)

Adds support for:
- plowingthroughlife.com (863)
- onceuponachef.com (864)
- tidymom.net (865)
- themagicalslowcooker.com (867)
- fattoincasadabenedetta.it (868)
- waitrose.com (869)
- eatwell101.com (866)

Drops support for python<=3.7.

Adds support for:

* Costco (850)
* ErrensKitchen (854)
* GrimGrains (846)

Other changes:

* Type-consistency fixes for the `scraper.instructions()` method -- this should always now return a `str` value. (852)
* NibbleDish: fixup in cases where `schema.org` ingredient text has been munged into a single string in the page's metadata. (856)
* Gousto: fixups for description, time and yields fields (853) and fix paragraph/linebreak handling (847)
* Dropped support for Python3.7 (that version has reached end-of-life) (857)
* Some misc small fixes discovered during development of pull request 852 (860)

With thank yous to daniel-tp jknndy shantih19! :tada:

- Adds support for tofoo.co.uk (836)
- realsimple: fixups for ingredients and yield fields (839)

With credit to jknndy and jbelluch! Thank you both.

- Omnivores Cookbook: fix handling of ingredient lists that involve multiple Wordpress Recipe Maker ingredient groupings (834)

With credit to ckid50!