There should be no need for a `stonemask` after `harvest`.

[Hiroshiba]

In the sample of demo.py, stonemask is performed after harvest, but since stonemask is supposed to be used only for dio, it may be less correct if it is.

Python-Wrapper-for-World-Vocoder/demo/demo.py

Lines 88 to 91 in 3a7c99a

	_f0_h, t_h = pw.harvest(x, fs)
	f0_h = pw.stonemask(x, _f0_h, t_h, fs)
	sp_h = pw.cheaptrick(x, f0_h, t_h, fs)
	ap_h = pw.d4c(x, f0_h, t_h, fs)