(refs #15) Escape quotes in shell commands.
(refs #35) Add lm.
Add a function `join'. It joins a list of sequences into a sequence with inserting an item in between each sequence.

Example:
  (join #\Space '("Hello" "World"))
  ;=> "Hello World"

  (join '-- (map #'list (iota 5)))
  ;=> (0 -- 1 -- 2 -- 3 -- 4)