Bread 2 represents a significant overhaul of Bread's internal structure.
It used to be that Bread parsed and unpacked an entire binary structure into a Python object on `parse`, and completely packed that structure up again on `write`. That wasn't the best design, especially in structures that have hundreds to thousands of tiny integers in them.
Bread now lazily loads fields and caches them. These two things should make it much faster to write and read large structures.