In ocaml write a function group of type int list -> int list list that groups adjacent equal numbers into lists.

For example,

group [1; 1; 2; 2; 1; 3] is [[1; 1]; [2; 2]; [1]; [3]]

group [1; 1; 1; 100; 100; 1] is [[1; 1; 1]; [100; 100]; [1]]

group [10; 10; 10; 10; 10] is [[10; 10; 10; 10; 10]] (one big group)

group [] is [] (nothing to group!)