Restrict the use of the ubyte helper function
Rename ds to xb
Add a XiaoBoard setter function
Use the new setter
Add a new XiaoBoard ctor
Need this signature in board
Add XiaoBoard ctor contracts
Now ready for complex board movegen testing
Update the movegen test data containers

 - Shorten the names of the ray containers.
 - Add an opponent and friendly blocker container.
Complete the sliding piece blocker test data
Add the other pieces
Work on a format for testing blocking movegen

Refactored all xiao-related stuff into a separate module 'xiao'.
This fixed a circular import issue that appeared with the
functionality added in this commit. With the stuff added in this
commit it is now possible to compute blocker movegen test data.

Writing out the test data by-hand versus computing the values is
balancing a trade-off between the complexity versus understandability
of both. The style adopted in this commit may strike a good
middle-ground. Further work will show any needed adjustments.
Change the xiao board ctors to be variadic functions
Explain what SinglePieceDestinations means
Add new test data

All test data for friendly blockers for king, knight, and pawn moves.
Pawn two-forward moves behave a bit like sliding moves so they are
defined separately from the rest.

Sliding moves take more precision as destination squares on the
opposite side of the blocker cannot be included.

In this commit testing of the attack boards was removed. The
algorithm that had been used to accumulate the value to compare
against the properties in Board was too simplistic to work with
multiple pieces on a board. A more complete solution is needed.
Start the work on defining the sliding friendly blocker test data
Shorten the destination test data container name
Generalize the test data construction
Trim some white space to make the definitions horizontally shorter
Add some new test data

Try out a new formatting style. The style needs to work with
the pattern of code for all of the test data to make it easy to
visually inspect the quality of the code.