Until now the footnotes section was parsed but not included in the resulting
AST - his required rebuilding it in the OrgWriter. It feels cleaner to include
it in the AST and only exclude it in the export
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.
until now buffersettings were always appended using \n which means the first
value would already be written as "\nVALUE". Not anymore.
Also we finally add an option to parse just the front matter. Still not
efficient as we tokenize the whole org file but i don't think saving a few
milliseconds would be worth making the code uglier.
