Updated README because of logrotate and minimum required compiler
ifdef for SIGUSR1, as this is only useful on __linux__
Added some basic code for multithreaded logging

Signed-off-by: Christian Rapp <crappbytes@gmail.com>
File was not saved before last commit :/

Signed-off-by: Christian Rapp <crappbytes@gmail.com>
Major improvements for the logger lib.
I added an optional background logger thread that uses a threadsafe queue. This way logging is much faster and your application will no longer block until the data is written to the streams. The disadvantage of this mode is the message might have a slight lag until they will be written.
We have an internal representation of a log message now. The struct LogMessage was needed because of the background logger.
The logger is now able to print a stacktrace for applications compiled with gcc or llvm. This not perfect yet especially there is no demangling for c++ implemented yet. But we need room for improvement ;)
We now need to link the Library against the threading library

Signed-off-by: Christian Rapp <crappbytes@gmail.com>