Add node::{width,depth,cycle}_u to access unknown<>s

These allow access to these fields while keeping their unknown type
with them.  This is nice when you junt want to blindly copy some
values.
Add flo::add_op

This allows me to add an operation to a flo structure.
Add operation::sources()

This iterates through all the sources in an operation.  It's slightly
easier than parsing out the operands() iteration.