Since writers are normally only used synchronously (i.e. to write one document
at a time), we don't guard modifications to their internal
state (e.g. temporarily replacing the string.Builder in WriteNodesAsString)
against race conditions.
The package global `orgWriter` and corresponding use cases of it (`org.String`,
`$node.String`) break that pattern - the writer is potentially used from
multiple go routines at the same time. This results in race conditions that
manifest as error messages like e.g.
could not write output: runtime error: invalid memory address or nil pointer dereference. Using unrendered content.
Additionally, since we catch panics in `Document.Write`, the corresponding
stack trace is lost and dependents of go-org never know what hit them.
As using a writer across simultaneously across go routines is not a standard
pattern, we'll sync the use of the global `orgWriter` instead of trying to make
the actual writer threadsafe; less code noise for the common use case.
WriteNodesAsString is simple enough to implement but exposing it is helpful in
the implementation of extending writers and we don't aim to keep writer a small
interface so let's expose it.
Being able to very easily get the original [1] Org mode content seems like
something that will come up quite often and is very little code.
[1] it's not really the original content, but rather the pretty printed version
of that - as the semantics don't change it shouldn't matter.
this introduces the PropertyDrawer node to make it easier to access the
properties associated to a headline - normal drawers don't parse their content
into kv pairs
- drawer entries without value were printed as FOO rather than :FOO:
- account for differences between raw & non-raw block:
raw blocks are not wrapped in a further element, just raw text & line breaks:
-> the first line has to be indented manually
non raw blocks do not end in a linebreak newline -> the END_BLOCK line has to
be indented (rather they end with a manual newline from another element)
