Key for the key-value data in Replicator. The type of the data value
is defined in the key. Keys are compared equal if the id strings are equal,
i.e. use unique identifiers.
Specific classes are provided for the built in data types, e.g. ORSetKey, and you can create your own keys.
trait Serializable
class Object
trait Matchable
class Any
class FlagKey
class GCounterKey
class GSetKey[A]
class LWWRegisterKey[A]
class ORSetKey[A]
class PNCounterKey
class PNCounterMapKey[A]