streaming result support

[clach04]

Currently no results are returned until search/scan has completed could yield results iteratively (so initial results are visible sooner).

• Would likely be useful for web browser clients - which inherently support streaming
• Not likely to be useful for OPDS clients

Possibly inconsistent with template idea in https://github.com/clach04/webook_server/issues/1

Status:

• ✅ Recent file results (recently added/modified files/ebooks) is streamed to OPDS and Browser client
• filename search
  • ✅ results are streamed to Web Browser clients
  • 🔴 NOT to OPDS 😿 - TODO checkout recent-files code and refactor (potentially refactor recent and search into same function?)
• 🔴 browsing is not streamed to either OPDS or Browser client 😿 - TODO checkout recent-files code and refactor

NOTE web browser benefit from initial quicker results. Unclear if KoReader (and other OPDS clients) will take advantage of streamed results.

[clach04]

Implemented in browser support that is present in dual OPDS / browser server #21 and https://github.com/clach04/webook_server/issues/23