v2.1-rc0

Same as with libnvme, after the initial 2.0 release, we got a lot of small bug fixes all over the place. This is also the main reason to release v2.1 relatively quickly. Let's get these fixes out the door.

Noteworthy changes:

• build and install fixes/improvements
• documentation fixes
• version reporting includes library version
• various fixes reported by coverity
• license clarification. The overall license is GPL-2.0-only (it stated GPL-2.0-or-later but a handful of files are GPL-2.0-only)
• new solidigm plugin

A big thanks to everyone who contributed to this pre release!