* doc/org-manual.org: Add `:tree-type month' option for capture
templates.
* lisp/org-capture.el (org-capture-set-target-location): Add
`:tree-type month' option to capture templates to group entries by
month.
* lisp/org-datetree.el (org-datetree-find-month-create): Add
`org-datetree-find-month-create' function to add datetree entries
grouped by month.
* testing/lisp/test-org-datetree.el
(test-org-datetree/find-month-create): Add test for new function.
* lisp/org-datetree.el (org-datetree-find-iso-date-create): New function.
(org-datetree--find-create): Support fixed text for insert.
(org-datetree-insert-line): Support fixed text for insert.
* testing/lisp/test-org-datetree.el (test-org-datetree/find-iso-date-create):
New test.
ISO week trees order dates by week and not by month.
* lisp/org-datetree.el (org-datetree--find-create): New function.
(org-datetree-find-year-create, org-datetree-find-month-create,
org-datetree-find-day-create): Removed functions
(org-datetree-find-date-create): Use `org-datetree--find-create' instead
of removed functions. Use calendar extract functions.
(org-datetree-insert-line): Do more formatting in `format-time-string'
since we call it anyway
* testing/lisp/test-org-datetree.el (test-org-datetree/find-date-create):
Test if new entries are put at the right place.
* lisp/org-datetree.el (org-datetree-find-date-create): Ignore case and
discard false positives (e.g., a fake property in an example block).
* testing/lisp/test-org-datetree.el: New file.
