Need to add examples of flat and stroked button to documentation

[andreyjamer]

Bug, feature request, or proposal:

Today, I noticed with surprise, that there are 2 new types of buttons: flat and stroked.
I read change log inattentively and looked on examples in documentation.
But there are no examples of these buttons.
It would be great if you will add them.

[FrederikSchlemmer]

Examples of the new buttons would be great!

I'll get this done!

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