Added DEFAULT_CODECS dict attribute to AudioSegment class

Conflicts:
	pydub/audio_segment.py
remove debugging line
fix typo
maintain backwards compatibility for AudioSegment.ffmpeg attribute
add rudimentary support for playback via ffplay/avplay
Merge branch 'master' of github.com:jiaaro/pydub
add a method for generating a silent audio segment of arbitrary duration
fix silence generation and support for 8bit audio
Fixed merge conflits from upstream