- we can't just look at the len of the string (~ #bytes) - that breaks down for
tables containing characters consisting of multiple bytes. This handles
more (still not all) cases and is good enough for now
- add _ to allowed tag chars - also require space between headline and tags
- links (link itself, not the description) spanning multiple lines are not
supported - otherwise we would have to take care of splitting link and adding
indentation for org pretty printing - and that sounds like such an edge case
that it seems cleaner to forbid them
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.
