[ANN] Small improvements in Columns view

[Nicolas Goaziou <mail@nicolasgoaziou.fr>]

Hello,

It is now possible to use custom summaries in Columns view, and re-use
the same property in multiple columns.

In the latter situation, the first columns referencing the property
determines how the values for that property are to be computed.

The following example illustrates these features:

  (defun my-Med (values printf)
    (let ((v (sort (mapcar #'string-to-number values) #'<))
          (l (length values)))
      (number-to-string
       (if (= (% l 2) 1) (nth (floor l 2) v)
         (let ((m (/ l 2)))
           (/ (+ (nth m v) (nth (1+ m) v)) 2.0))))))

  (defun my-Q1 (values printf)
    (number-to-string
     (nth (floor (length values) 4)
          (sort (mapcar #'string-to-number values) #'<))))

  (defun my-Q3 (values printf)
    (number-to-string
     (nth (floor (* (length values) 0.75))
          (sort (mapcar #'string-to-number values) #'<))))

  (add-to-list 'org-columns-summary-types '("Med" . my-Med))
  (add-to-list 'org-columns-summary-types '("Q1"  . my-Q1))
  (add-to-list 'org-columns-summary-types '("Q3"  . my-Q3))

  #+COLUMNS: %ITEM %VALUE(Min){min} %VALUE(Q1){Q1} %VALUE(Med){Med} %VALUE(Q3){Q3} %VALUE(Max){max}
  * H   
  ** S1 
  :PROPERTIES:
  :VALUE: 2
  :END: 
  ** S2
  :PROPERTIES:
  :VALUE: 1
  :END: 
  ** S3
  :PROPERTIES:
  :VALUE: 9
  :END: 
  ** S4
  :PROPERTIES:
  :VALUE: 7
  :END:


Feedback welcome.

Regards,

-- 
Nicolas Goaziou                                                0x80A93738