distinct add from add_with

we were trying to be too smart in checking if the value given was a
function or not in `lru:add/3` and `lru:contains_or_add/3` functions.
Instead we now have distinct `lru:add_with/3` and `lru:contains_or_add_with/3` to
pass a function.

fix #2
1 job for master in 51 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #5422742
test

00:00:51