Make library signal safe

At the moment logc is not signal safe. This includes configuration calls from signals as well as _log calls. Problem is not only atomic operation but also sharing of output. There can be log in progress when signal is received. We can't use locks as we would be waiting in signal to for release that would never came as signal handler would never be exited. Ignoring lock can lead to output mixing.

• prevent signal handling when outputting message
• suggest no modification of log configs from signals or investigate if atomic objects can prevent problems