Add identifier for releases with multiple compatible assets

[oeb25]

This change is relevant when you have multiple binaries as part of a single release. In this case, the target is not enough to determine which asset to choose. Thus this change allows an identifier to be passed along from the builders, to select the correct one in such cases.

This adds argument identifier: Option<&str> to Release::asset_for, which allows the caller to specify a string that must be part of the asset name in addition to the target.

Additionally it adds a method to ReleaseUpdate which allows the identifier to be specified in the UpdateBuilder structs.

One possible change, could be to make the identifier a closure, or like the Pattern like the struct search functions in std, instead of relying on only substrings.

[jaemk]

Looks good

[jaemk]

released in 0.35.0

[oeb25]

Thanks 🎉