DOC: add docstring for the thresholding module.
DOC: add docstring for the thresholding module.

kwohlfahrt/pywt,aaren/pywt,grlee77/pywt,grlee77/pywt,Dapid/pywt,rgommers/pywt,PyWavelets/pywt,michelp/pywt,ThomasA/pywt,eriol/pywt,Dapid/pywt,michelp/pywt,rgommers/pywt,kwohlfahrt/pywt,michelp/pywt,aaren/pywt,aaren/pywt,Dapid/pywt,eriol/pywt,rgommers/pywt,rgommers/pywt,kwohlfahrt/pywt,ThomasA/pywt,eriol/pywt,PyWavelets/pywt,ThomasA/pywt