update traps documentation (unfinished)

update traps documentation (unfinished)

* doc/ref/Makefile.am:
* doc/ref/guile.texi:
* doc/ref/scheme-debugging.texi: Remove scheme-debugging.texi, which
  only described tracing. Tracing documentation is now in
  api-debugging.

* doc/ref/scheme-using.texi (Evaluating Scheme Code): Remove reference
  to source traps, as that section is going away.

* doc/ref/api-modules.texi (Included Guile Modules): Remove reference to
  Tracing. This section is a little silly, anyway...

* doc/ref/api-evaluation.texi (VM Behaviour): Remove section, it is in
  api-debugging now.

* doc/ref/api-debug.texi (Stacks, Frames): Rename sections from
  "Examining the Stack" and "Examining Stack Frames", respectively.
  (Traps): Update for current API. A big and not-quite-finished update.