specifying workbook dir for dist-hook

[Thien-Thi Nguyen]

Rob,

since we're moving TODO and BUGS (and maybe in the future other things)
out of guile-core/ into workbook/, it behooves us to figure out how to
get these files back into the tree on release.  apparently, automake
supports "dist-hook", which we currently use in these makefiles:

  ./doc/Makefile.am
  ./guile-readline/Makefile.am

it is easy to add something like:

  dist-hook:
          @echo doing dist-hook...
  if MAINTAINER_MODE
          @echo 'This is a snapshot of the TODO file.' > TODO
          @echo >> TODO
          cat $(workbook)/tasks/TODO >> TODO
          $(workbook)/../scripts/render-bugs $(workbook)/bugs > BUGS
  endif

to top-level Makefile.am.  the question is how to define $(workbook)?
we can either require maintainers to specify this directory like:

  make workbook=some/path/to/workbook dist

or adopt the convention that workbook is always at
$(top_srcdir)/../workbook and codify that in Makefile.am.

so: what is your preference?
    what other files can we factor out of guile-core/?
    where would we put them in workbook/?
    where is a good place to document all this?  (RELEASE?)

if you see where i'm going w/ this, you can obviously make the changes
yourself, but i'm happy to do them for you if given reasonable answers.

thi