Description
It seems unnatural that CollectionAllocErr currently does not implement std::error::Error which would come in handy in cases such as implementing std::error::Error::source on user-defined errors caused by CollectionAllocErr.
While error_in_core is not stable yet, such implementation could be hidden behind a feature flag such as (commmonly used) std.
Since the features should be additive (i.e. an inverted no-std feature would not be the right approach), it is a breaking change to add such a feature so I suggest adding this to #183.
If this change is welcome, I may create a pull request to implement it.
cc @mbrubeck as the maintainer of the 2.0 wishlist