Release 0.4.1

• Fix bug of extend mode result in a change of dtype (from the default f32 to f64). Now it is fixed at f32.
• Add convolve() method. A convolution method (default to fft). Now you can apply reverb, do autocorrelation to the signal. (#40)
• Update Ugen docstring and remove deprecated variable names (#39)
• namespace improvement.
• sanic and notebook are now optional: If you plan to use JupyterBackend, install pya with pip install pya[remote] (#38, #41)