Transparently rework Logging mechanism. This now allows to redirect the logging
into any desired stream, e.g. a file by setting:
	FILE* pFile = fopen("pxar.log", "a");
        SetLogOutput::Stream() = pFile;
or could be catched by the GUI to display log messages in a window. The stream
can be changed whenever wanted (e.g. switching from the default stderr to a file
after the user entered a filename)
Merge branch 'master' of github.com:psi46/pxar
API EXTENSION: For convenience, add maskColumn(col) function to the DUT.
Does the same as maskPixel, but for all pixels in that column.