Improvements to import, export and serialize

Would you be open to a PR that brings the following functionality?

• serialize + inject support for Documents
• export and serialize cfg (including custom handler functions) for both Index and Document then import/inject either to existing index/document or auto create Index/Document from the cfg container in the export.
• add optional compression to export and decompression on import
• export to Blob rather than JSON

I've implemented most of it now with tests, but I'm sure it could benefit from your review - especially for some of the Document stuff