How do we add extensions functions on top of the current DSL?

[Initial pass to a Free based DSL built on `kategory`](https://github.com/Guardiola31337/uiagesturegen/pull/1) follow up questions:

- How do we add extensions functions on top of the current DSL? Is it the best way to go or should new functionality be included in the DSL? Pros? Cons? How do we decide which approach to chose?

cc/ @raulraja 