0.5.0

CHANGES:

• Add Repr.int63, a representation of the Optint.Int63.t type (provided by
  the optint library). (#80, @craigfe)

• Change Repr.{like,map,partially_abstract} functions to not require _ staged wrappers around any (monomorphic) overrides. (#77, @craigfe)

• Fix a bug causing custom Repr.{random,random_state} implementations to be
  ignored. (#79, @craigfe)

• Fix Repr.pre_hash to rely on itself recursively. This ensures that custom
  pre_hash functions attached to components of larger types are not ignored.
  (#71, @craigfe)