- In this version of the intlist + avgwrdlen example, the
  list-of-integers module (intlist.c and intlist.h) and
  it's test program (testlist.c) have been moved into the lib
  directory and made into a library - with it's own Makefile.

- the Makefile in the lib directory builds two things:
  	- the executable testlist for us to test that intlist works
	- the library libintlist.a containing intlist.o

- all that remains in this top level directory is the real main
  program (avgwordlen.c), a set of shared definitions in defns.h,
  and a Makefile that tells the C compiler to search for includes
  in the lib directory (-Ilib in CFLAGS), and to search for libraries
  in the lib directory (-Llib in LDLIBS), and to link libintlist.a in
  (-lintlist also in LDLIBS).

- note that dependendencies on intlist.h have completely gone.

- note that I've added a "libs" target to run make in lib (cd lib; make),
  and described libs as a target to build in BUILD.  no file called
  "libs" is ever built, so make will always run the "cd lib; make" action,
  however that inner make will do no work if everything's up to date
  in the libs directory.

- note also that I've added a new clean target "spotless" to make clean
  in both directories, some would prefer "clean" to do that too.

- so, to build, as before, type 'make' and you'll notice it first cd into
  lib and run make there - compiling intlist.c, testintlist.c, linking
  them together and then creating libintlist.a via ar and ranlib.

- but still, libintlist.a is a solid part of this codebase.  What if we
  wanted to split libintlist completely from applications like avgwordlen
  that happened to USE libintlist?  see 05.libintlist and 06.avgwordlen
  for that..
