Prevent files with excluded FILETAGS from being exported

[Thomas Ingram]

Hello,

Currently when trying to export an org file with FILETAGS set to
"noexport" (or any value in `org-export-exclude-tags') the file is still
exported with the title and top level text.  I propose that be changed
so files with FILETAGS in `org-export-exclude-tags' are completely
skipped by the exporter.

This would be extremely useful in combination with ox-publish, as it
would allow users to easily exclude files from publishing from within
the file.  Currently this can only be done by adjusting the ':exclude'
value to match the filename in the `org-publish-project-alist' settings.

Please let me know your thoughts.  I would be happy to try to submit a
patch but I would need some pointers on where in the export process this
change should be added.

Thanks,
--
Thomas Ingram
https://taingram.org