* contrib/lisp/org-odt.el (org-odt-is-formula-link-p):
Recognize *.mml and *.mathml as mathml files. Recognize *.odf
files as OpenDocument formula file.
(org-odt-copy-formula-file): Use `org-odt-zip-extract-one' to
handle ODF formula files.
(org-export-odt-format-formula): If a ODF formula link has no
caption or label, embed it inline. Otherwise embed it as
displayed.