Add `Display` to signature types

[ggutoski]

Need Display trait bound for

• jf_primitives::SignatureScheme::Signature
• <Signature as TryFrom<TaggedBase64>>::Error

@QuentinI please add what you need to this issue.

[mrain]

Could you explain the use case here? Most of the actual Signature structs already have Display derived from tagged macro.

[QuentinI]

@mrain

Could you explain the use case here? Most of the actual Signature structs already have Display derived from tagged macro.

HotShot abstracts over some types, including Signatures, where it requires SignatureScheme, which means if hs-builder-core wants to abstract over those as well, it cannot rely on specific types' Display implementation. I'm asking for new bounds in SignatureScheme:

• SignatureScheme::Signature: Display
• <<SignatureScheme::Signature> as TryFrom<TaggedBase64>>::Error: Display (or <SignatureScheme::Signature>: TryFrom<TaggedBase64, Error=Tb64Error>, since Tb64Error is Display and every Signature probably already uses Tb64Error)