org-colview: Allow custom COLLECT functions for derived properties
* lisp/org-colview.el (org-columns-summary-types): Allow new format.
(org-columns--summarize): Update to new summary type format.
(org-columns--collect): New function.
(org-columns--compute-spec): Apply changes.
* testing/lisp/test-org-colview.el (test-org-colview/columns-summary):
Add test.
In addition to (LABEL . SUMMARIZE), org-columns-summary-types now
accepts (LABEL SUMMARIZE COLLECT) entries. The new COLLECT function is
called with one argument, the property being summarized.
TINYCHANGE