Write key/value pair into a FIFO list.
write-fifo adds a key/value pair to the FIFO <list>, specified with string <key> and <value> (in
"key" and
"value" clauses). It always adds data to the end of the list. <value> is a pointer to any type, allowing storage of any kind of data. <key> and <value> must not go out of scope or be freed while FIFO is used - if necessary, store a copy (see
copy-string for strings).