Remove unused LeanThriftFact
Add ThriftDerserializationBehaviourSpec to demonstrate clear behaviour
Only set ThriftFact seconds if not zero
Add behaviour spec for thrift fact seconds size
Remove ThriftSerialiser.fromBytes as it was doing a deep copy

We can _never_ allow this to be called accidentally
Add extra clearUnsafe test to ThriftDerserializationBehaviourSpec
Use ThriftSerialiser for everything - no exceptions
Merge pull request #199 from ambiata/topic/thrift-clear-spec

Add ThriftDerserializationBehaviourSpec to demonstrate clear behaviour