ENH: `styler.format` options
- [x] adds to #41395 
- [x] add options
- [x] add tests
- [x] update `Styler.format` docstring
- [x] update `options.rst`
- [x] update `Styler` init docstring
- [x] whatsnew

update user guide **will be a follow-on when all options are merged**

![Screen Shot 2021-08-28 at 13 26 44](https://user-images.githubusercontent.com/24256554/131216430-ef0a76bc-7ae7-4576-aa05-c684b13db67a.png)

thanks pls check the options on the issue :-> > looks good. technically this could break code if some actually uses `pd.set_option('precision')` for example but that will now raise so prob ok.

the docs do advise against that behaviour for this specific reason, so I think ok.