Added FdbSubspace.Partition( ITupleFormattable )
Subspace are now based on a binary prefix [BREAKING CHANGE]

- Usually the prefix is also created from a tuple, but it is not a guarantee
- Tuples created from a subspace are "relative" to the tuple
- Added new FdbSubspaceTuple that link the created tuple to the parent subspace
- Tuples created from a subspace will include the subspace binary prefix when packed.
- The same subspace must be used to unpack the keys.
- subspace.Tuple property is gone. You can use subspace.ToTuple() to create a new empty Tuple and append to it.
- added back Pack(IFdbTuple) and Append(IFdbTuple) that will work as intended
Follow up on subspace refactoring (breaking change)

- All methods that return a tuple renamed to "Create(...)".
- Added version of Concat/Extract that take arrays of keys
- fixed/updated the comments
Renamed db.Namespace into db.GlobalSpace and support for binary prefixed global spaces

- The default subspace of the db can be set to any arbitrary binary prefix, not just tuples
Fixed directory layer

- prefix is now a slice and cannot be == null
remove the test db prefix when dumping subspaces in unit tests