Clarify 'DOI' as 'Publication DOI' in log message
Fixes for sequencelinkout*.xml sizes

Reworked save() to split files in the middle of an object list.

Still has a lot of if/else handling, would be better suited by using an
XML library and a stack.

Fixes #18
Only suppress close tags if changed on last file
Update comments
Merge pull request #9 from datadryad/file-splitting

Fix file splitting on sequencelinkout files