* lisp/ox.el (org-export-expand-include-keyword): Change parsing so
that arbitrary blocks around the included content can be used.
Content is not code-escaped unless it is a literal block, this
applies to "src" and "example".
* doc/org.texi (Include files): Document the additional markup.
* testing/lisp/test-ox.el (test-org-export/expand-include): Add test
for an #+INCLUDE with "html" and "center" markup.
* testing/examples/include.html: New file, used for testing
"#+INCLUDE html".
Achim Gratz