implemented some functions for m3u block. shared library has unresolved symbols because of fvisibility flag in gnuradio build.
fixed unresolved symbol error. needed to copy the gnuradio-internal wavfile.h/.cc into the drm source tree because of disabled symbol visibility in the gnuradio build. renamed the file and integrated it in the drm namespace to avoid ambiguities.
m3u and wav files are successfully opened now.
bugfix