Is this library stable? If not, when stable version will be released?
It depends on what you mean by stable.
If you mean the API, then probably you can safely say it's stable. I don't plan any (big) changes in the API. As for the binaries, it is binary compatible.
If you mean performance, I suppose it's stable enough. I have a project deployed with it and hadn't had any problems yet. Also it was reported by @madababi that the library works fine on Raspberry PI (with proper cross-compiling of course). There's always the possibility of minor bugs, but it should be fully functional.