[IconButton] add callback signatures to docs

[theosherry]

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

Hey, PR for #3096 .

[oliviertassinari]

element

[theosherry]

Oops sry. Fixed the typo.

[mbrookes]

Thanks for continuing through these, it's really appreciated!

Would you be happy to standardise the wording on the other prop descriptions while you're there? If you do you can squash onto this commit.

[theosherry]

@mbrookes No problem. I'll give it a go when I get home tonight.

[mbrookes]

Thanks! 👍

[theosherry]

Ok, let me know what you think. I tried to be consistent with what I've done so far.

[mbrookes]

Thanks @theosherry - I should have mentioned it (but I assumed you were already working from it as your callback changes were in line): https://github.com/callemall/material-ui/wiki/Documentation#description-wording

Could you follow the 'If true, ... ' pattern for the bools? And perhaps double check the others?

Doesn't have to be word for word, as there are inconsistencies everywhere due to how Material-UI has evolved, but the more cleanups the better!

[theosherry]

Of course. Sorry, I forgot about those guidelines.

[mbrookes]

Thanks, looks good! 👍

[alitaheri]

Thanks a lot @theosherry 👍