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.