This is largely a maintenance update to ensure the SDK is up-to-date.

Features:
* Markdown is now rendered if "Markdown: yes" was passed (#310, thanks to @NiNiyas for reporting)
* You can now disable UnifiedPush so ntfy does not act as a UnifiedPush distributor (#646, thanks to @ollien for reporting, and to @wunter8 for implementing)

Bug fixes + maintenance:
* Subscriptions without icons no longer appear to use another subscription's icon (#634, thanks to @topcaser for reporting, and @wunter8 for fixing)
* Bumped all dependencies to the latest versions (no ticket)
