New: add 3 new pre-defined Lutin operators: 'nor', '#', and n-ary xor

nb: the infix binary 'xor' already existed.
nb2: xor (and so #) can be costly
2 jobs for 2.69.0 in 9 minutes and 51 seconds
latest
Status Job ID Name Coverage
  Build
passed #89942
build

00:05:44

 
  Test
passed #89943
test_opam_test

00:04:06