Define a standard set of toString format specifiers

Each User Defined Type will implement the following set of format specifiers
 - `%s` = a human-readable serialization
 - `%d` = a diagnostic serialization, useful for debugging

The following UDT's will be updated
 - `Board`
 - `XiaoBoard`
 - `Surface`
 - `MoveList`
 - `BoardStatus`