Collapse versioning directives

[JacobCoffee]

In some libs like Flask or Click (?) when there are multiple versioning directives they are collapsed into a dropdown.

e.g.,

.. versionadded: 1.0 would just be visible, but

.. versionadded: 1.0
	New thing

.. versionchanged: 1.1
	Changed thing
	
.. deprecated: 2.0
	No more thing

Would be collapsed.

Currently we get just a bunch of admonitions:

it would be cool to autodetect multiple and throw them into sphinx-dropdown (or even prettier, sphinx-togglebutton)

[lepture]

It would be better to create a sphinx extension to group the version changes into a <details> DOM.

[JacobCoffee]

that makes sense!