src_cpp: update dataflow parser
external: fix memleak in smarc
DataFlow : support stringify,loads; fix memleaks

fix memleak in freeOutputFormatDescription
src_python: Dataflow: support pickling
src_python: update doctest
MP3FileReader: TrimBeginningSilence is not supported anymore
yaafe-io: improve MP3FileReader
yaafe-io: AudioFileReader: support TimeStart, TimeLimit