Feature request: overlapping sections

[jberger]

Related to #9 (and only really useful if that is included), it is sometimes helpful to have sections that overlap. If the end tag were end-sample(name), even optionally, then that would be allowable. I don't know how much harder that makes your parser. Certainly you'd want #9 because if sections overlap then there will definitely be markers visible in the rendered version. Once again if this isn't something you're amenable to I can use line numbers and it is no great loss.