Improve comments in import_item()
Remove JSON_PRETTY_PRINT as this requires PHP 5.4+
Change default export file extension from XML to JSON
Add file-level phpDoc to export.
De-duplicate code when checking for taxonomies
Update phpdoc for $taxonomy_package property
Set up name for package taxonomy in Importer constrictor
Switch importer->file_term_id property into an array for general use

Gives a handy store for general file meta for use elsewhere.
Add file docblock to file_meta

Will be used later to fetch file-scope docblock tags
Fix silly typo. Antiprops @paulgibbs
Workaround for a WP core bug where hierarchial taxonomy caches are not being cleared
Add items to package taxonomy during import
Set better rewrite slugs for package and since taxonomies.