v6.1.0

Added

• Type families: custom behaviour for every type matching a predicate,
  where RegisterCustomEqual and friends are custom behaviour for one
  concrete type. deep.RegisterTypeFamily takes a Match predicate and a
  family of handlers — Equal, Clone, Diff, Apply, and a value codec — and any
  type the predicate accepts is handled by them, however many such types
  exist.

  The distinction matters for types produced by another runtime. A protobuf
  application holds hundreds of generated message types; registering each one
  is not a usable interface, and every one needs the same treatment. A family
  is also all-or-nothing about its boundary: once a value is matched, nothing
  generic looks inside it — an operation whose path crosses into a matched
  value is handed to the family's own applier with the remainder of the path,
  and the family's codec carries its values on the wire in their own form.

  This is the extension point the deep/proto companion module builds on; it
  is proto-agnostic and serves any foreign type family with its own runtime.