Merge pull request #46 from yipdw/development

Set the common part of an item's data_dir in the pipeline
Uses better unique id generation scheme (ArchiveTeam/seesaw-kit#45).
Bump version to 0.1.4b1.
Fixes --max-items, recursion depth exceeded. Closes ArchiveTeam/seesaw-kit#39.
Fixes regression with --max-items.
Works around spurious item events. Closes ArchiveTeam/seesaw-kit#27.
Bumps version to 0.1.5b1.