Convert "offset" into an overload
Convert "label" to overload
Convert "form" and "parent" into overloads
Make restoring iostream flags exception-safe
Rename dwop_f to die_op_of, adjust functionality accordingly

- The dwop_f approach had a problem that an op that didn't support all
  possible branches would silently fail when presented with an
  unsupported value.  Better just have this as overloads--that's easy
  to set up as well, has error messages that scale reasonably, and is
  more future-proof WRT new value types.
Annotate position of values in location list
Drop @number, @number2, add an overload of value to do this
Convert "child" to an overload
Add a dedicated type for location expression element and address range

- Location lists are represented as a bunch of elements that a
  location-like attribute accesses.  Each of these elements has an
  address (actually an address range) and a bunch of children, which
  are the location expression operations.