simu & legacy - more primtives for pair manip
ex 5.22 - append and append!
ex 5.22 - append impl
ex 5.22 - works on simu.scm
ex 5.22 - last-pair impl
ex 5.22 - last-pair tested
ex 5.22 - impl my-append!
ex 5.22 - prepare testcases
ex 5.22 - done