Until now we expected the .org file to print back to itself - we can't do that
when the input is not pretty printed already - with the introduction of blocks
with unindented content that will be the case.
including org files is more complex - e.g. footnotes need to be namespaced to
their source file. org does this by prefixing each included files footnotes
with a number - but even that is not enough as it doesn't guarantee
uniqueness.
As I don't have a usecase for it, I'll avoid the additional complexity for
now.
