v0.21.0

• NOTE: Semi-counterintuitive change: using the a stride when slicing AudioSegment instances (for example, sound[::5000]) will return chunks of 5000ms (not 1ms chunks every 5000ms) (#222)
• Debug output from ffmpeg/avlib is no longer printed to the console unless you set up logging (see README for how to set up logging for your converter) (#223)
• All pydub exceptions are now subclasses of pydub.exceptions.PydubException
• The utilities in pydub.silence now accept a seek_stepargument which can optionally be passed to improve the performance of silence detection (#211)
• Fix to pydub.silence utilities which allow you to detect perfect silence (#233)
• Fix a bug where threaded code screws up your terminal session due to ffmpeg inheriting the stdin from the parent process. (#231)
• Fix a bug where a crashing programs using pydub would leave behind their temporary files (#206)