Inserts value in the list stored at key either before or after the reference
value pivot.
When key does not exist, it is considered an empty list and no operation is
performed.
An error is returned when key exists but does not hold a list value.
@return
@integer-reply: the length of the list after the insert operation, or -1 when
the value pivot was not found.
@examples
RPUSH mylist "Hello"
RPUSH mylist "World"
LINSERT mylist BEFORE "World" "There"
LRANGE mylist 0 -1