Improve description of `towncrier` `apichange` type

[tsbinns]

Problem

Changelog entries with the apichange type get description "API changes by deprecation", however this also encompasses API additions with no deprecations.

E.g., in the 1.11 changelog, the apichanges section shows the following:

Only #13398 involves a deprecation; #13350 and #13458 involve only new parameters.

Proposed Solution

I think the description of apichange could be made more general, e.g., just "API changes".

Could also have separate types for API deprecations and API additions, but there are cases where the deprecation of something is accompanied by the addition of a replacement, so separating those two doesn't always make sense.

[drammock]

I think the description of apichange could be made more general, e.g., just "API changes".

Agreed.

separating those two doesn't always make sense.

Agreed.

[tsbinns]

Opened a fix in #13794, but am just now realising that the PRs for new parameters are inconsistently labelled as apichanges and newfeatures.

Should it instead be the case that apichanges remains with the deprecation description exclusively for this purpose, and anything which is just a new parameter is labelled as newfeature?

[wmvanvliet]

Yes, I thought that adding functions/classes/parameters are newfeature, while removing or renaming existing functions/classes/parameter are apichanges. It's a bit confusing, because adding a parameter to a function is also an API change. So perhaps the existing formulation of "apichanges are for things that need a deprecation cycle" is actually what we want.

[tsbinns]

Yeah, closing #13794.

Perhaps it's worth simply making the descriptions more explicit in the contribution guide, e.g.:

apichange
Changes to existing code behavior that require a deprecation period. Can include the addition of new features only if existing code behavior is changed alongside this.

newfeature
For new features that do not change existing code behavior. If existing code behavior is changed alongside the addition of these features, the changes should instead be labelled as apichange.

Is currently:

apichange
Code behavior changes that require a deprecation period.

newfeature
For new features.