Support TryDeserialise and TrySerialise

[drewnoakes]

These versions should not throw, but rather return true/false.

bool TrySerialise(Stream, object)       // if false, stream is left in unspecified state
bool TrySerialise(UnsafePacker, object) // if false, packer is left in unspecified state
bool TrySerialise(object, out byte[])   // if false, byte[] is null

bool TryDeserialise(Stream)             // if false, stream is left in unspecified state
bool TryDeserialise(Unpacker)           // if false, unpacker is left in unspecified state
bool TryDeserialise(byte[], out object) // if false, object is null

Duplicate the above for the generic Serialiser<T> and Deserialiser<T>.

Before implementing this, consider whether the Stream/Unpacker overloads actually make sense. Leaving the streams in an unspecified state is basically unrecoverable. Consider the scenarios here.