Add Apply and Traverse for SortedMap

[johnynek]

see #1964 for more discussion.

[LukaJCB]

Wouldn't we get conflicting instances because SortedMap is a subtype of Map?

[LukaJCB]

So I tried this and it seemed to work just fine. Not sure why I thought it wouldn't work.

So I think we could get all the instances for SortedMap, that already exist for Map, but require an instance of Order[A] right?

Could potentially be relevant for #1831

[johnynek]

Maybe we need to make it higher priority? Or maybe not. Subtyping and implicit resolution confuses me sometimes with what is and is not ambiguous.

[LukaJCB]

We should probably also add instances for SortedSet while we're at it.

[johnynek]

+1

[LukaJCB]

Actually there can't be any instances for SortedSet, as that'd require an implicit Order [A] instance, when there is no actual A.

[kailuowang]

When there are multiple instances for the target type F's inheritance hierarchy, (but not the type class), the instance for the subtype is more "specific" I think.