README updated
fp/secd/secd.c: secdf_append() fixed

Previously secdf_append would do destructive append any time it found that xs has less than 2 references. This is not correct, because list_next(xs) may have more than 1 refefrence too. So, the desctructive append is possible only if all of list items are referenced less than 2 times.
Merge branch 'master' of github.com:EarlGray/language-snippets