New tree directory and Makefile. It is now possible to compile an example
by typing make <name_example> where <name_example> is "eight_queens",
"night_tours" or "us_map". make check1 compile and execute eight_queens
program. make check2 compile and execute knight_tours program. make
check3 compile and execute us_map program. The BDD library is linked as
a static library, to be included through #include <bddenv.hh>.
oldsrc deleted ...