QsLog version 2.0b1

Changes:
* destination pointers use shared pointer semantics
* the file destination supports log rotation. As a consequence, log files are encoded as UTF-8 and
the log appends rather than truncating on every startup when rotation is enabled.
* added the posibility of disabling logging either at run time or compile time.
* added the possibility of using a separate thread for writing to the log destinations.

Fixes:
* renamed the main.cpp example to avoid QtCreator confusion
* offer a way to check if the destination creation has failed (for e.g files)