lists are now a data type recognized by code blocks

lists are now a data type recognized by code blocks

* lisp/ob-ref.el (org-babel-ref-resolve): Recognize `list' as a unique
  type of data
  (org-babel-ref-at-ref-p): Recognize `list' as a unique type of data

* lisp/ob.el (org-babel-read-result): Recognize `list' as a unique
  type of data
  (org-babel-read-list): A function to read a textual Org-mode list
  into an emacs-lisp list.
  (org-babel-insert-result): Recognizes the "list" result param to
  insert data as an Org-mode list.
  (org-babel-result-end): Find the end of an Org-mode list.
  (org-babel-merge-params): Add "list" as a result param.

* doc/org.texi (results): Documentation of the new "list" results
  header argument.