org.el: Implement user-defined table sorting
* lisp/org.el (org-do-sort): Implement the ?f and ?F sorting options
to allow user-defined table sorting. Update the DOC string.
* lisp/org-table (org-table-sort-lines): Add the GETKEY-FUNC and
COMPARE-FUNC optional parameters and pass them to the call to
`org-do-sort'. Update the DOC string.
* doc/org.texi (org-table-sort-lines): Update documentation to reflect
the addition of the ?f and ?F options.
This patch implements user-defined extraction and comparison functions
for table sorting. Thanks to Nicolas Goaziou for helpful suggestions.
This patch was discussed on the Org Mode mailing list:
http://article.gmane.org/gmane.emacs.orgmode/93334