Sequence elements should be shown in brief form
Add support for attribute integration

- Attribute assertions now don't integrate by default.  Instead, an
  "integrate" edge is between a DIE and its abstract instances.  That
  has to be followed explicitly.  A number of idioms use the operator
  to emulate what libdw interfaces provide.

- I'm afraid this is too low-level.  Writing (integrate* @AT_name) is
  a bit mouthful, and incorrect at the same time (the fully correct
  form is ((!AT_name integrate)* @AT_name).  Writing this is bound to
  get old very quickly.  Some of that could be alleviated with a
  proposed semantics that use a block on TOS to drive the integration.
  One would then write, say, {@AT_name} integrate.  But that's still
  somewhat long-winded.  Something like I:{@AT_name} might possibly
  work.