Explicitly version for dependencies
Update gemspec
Update author's email
Redirect to present entry_path from entry.old_path

When entry.old_path present and someone accessed on it,
days will redirect to present entry_path.

- New column:
  entries.old_path (string, default: nil)
days import: Accept entry.old_path
days import: Allow omitting entry.id
Add tumblr_export.rb