Using config.h instead of compat.h

[amagura]

After looking at other projects out there that use autotools, I suspect that I'm using it wrong and over engineering ZBatt: for example, I noted that some projects seem to make use of a config.h file that autotools produces that (I assume) contains information about missing functions, headers, and that kind of thing.

I think that if I were to make use of config.h that I might be able to get rid of things like compat.h and use fewer checks in configure.ac, but who knows: I'd just like to take sometime to look into this and ensure that I'm using autotools correctly.