* lisp/ox.el (org-export-dispatch): Add customizable variables
`org-export-body-only', `org-export-visible-only', and
`org-export-force-publishing', and use them in `org-export-dispatch'.
* doc/org-manual.org (The Export Dispatcher): Document the new export
variables.
* etc/ORG-NEWS (New customization options for ~org-export-dispatch~):
Announce the new customization options.
Currently when calling `org-export-dispatch', two of the export
options can have their defaults specified with customizable variables:
"Export scope" (via `org-export-initial-scope') and "Async export"
(via `org-export-in-background'). This change adds customizable
variables for the "Body only", "Visible only", and "Force publishing"
options as well.