Fix a few golint issues.

The following golint issue is not fixed, as the error name EOS is given to mimic io.EOF.
	io.go:15:5: error var EOS should have name of the form ErrFoo

The following golint issues are simplifications:
	pcm.go:26:2: should replace f -= 1 with f--
	pcm.go:33:2: should replace s += 1 with s++

The following golint issues are related to comments and are fixed by using comments with the same structure asstrings.Reader.Seek:
	alaw.go:19:1: comment on exported method ALawSamples.Len should be of the form "Len ..."
	alaw.go:24:1: comment on exported method ALawSamples.Cap should be of the form "Cap ..."
	alaw.go:29:1: comment on exported method ALawSamples.At should be of the form "At ..."
	alaw.go:35:1: comment on exported method ALawSamples.Set should be of the form "Set ..."
	alaw.go:41:1: comment on exported method ALawSamples.Slice should be of the form "Slice ..."
	alaw.go:46:1: comment on exported method ALawSamples.Make should be of the form "Make ..."
	alaw.go:51:1: comment on exported method ALawSamples.CopyTo should be of the form "CopyTo ..."
	float.go:16:1: comment on exported method F32Samples.Len should be of the form "Len ..."
	float.go:21:1: comment on exported method F32Samples.Cap should be of the form "Cap ..."
	float.go:26:1: comment on exported method F32Samples.At should be of the form "At ..."
	float.go:31:1: comment on exported method F32Samples.Set should be of the form "Set ..."
	float.go:36:1: comment on exported method F32Samples.Slice should be of the form "Slice ..."
	float.go:41:1: comment on exported method F32Samples.Make should be of the form "Make ..."
	float.go:46:1: comment on exported method F32Samples.CopyTo should be of the form "CopyTo ..."
	float.go:64:1: comment on exported method F64Samples.Len should be of the form "Len ..."
	float.go:69:1: comment on exported method F64Samples.Cap should be of the form "Cap ..."
	float.go:74:1: comment on exported method F64Samples.At should be of the form "At ..."
	float.go:79:1: comment on exported method F64Samples.Set should be of the form "Set ..."
	float.go:84:1: comment on exported method F64Samples.Slice should be of the form "Slice ..."
	float.go:89:1: comment on exported method F64Samples.Make should be of the form "Make ..."
	float.go:94:1: comment on exported method F64Samples.CopyTo should be of the form "CopyTo ..."
	mulaw.go:19:1: comment on exported method MuLawSamples.Len should be of the form "Len ..."
	mulaw.go:24:1: comment on exported method MuLawSamples.Cap should be of the form "Cap ..."
	mulaw.go:29:1: comment on exported method MuLawSamples.At should be of the form "At ..."
	mulaw.go:35:1: comment on exported method MuLawSamples.Set should be of the form "Set ..."
	mulaw.go:41:1: comment on exported method MuLawSamples.Slice should be of the form "Slice ..."
	mulaw.go:46:1: comment on exported method MuLawSamples.Make should be of the form "Make ..."
	mulaw.go:51:1: comment on exported method MuLawSamples.CopyTo should be of the form "CopyTo ..."
	pcm.go:38:1: comment on exported method PCM8Samples.Len should be of the form "Len ..."
	pcm.go:43:1: comment on exported method PCM8Samples.Cap should be of the form "Cap ..."
	pcm.go:48:1: comment on exported method PCM8Samples.At should be of the form "At ..."
	pcm.go:53:1: comment on exported method PCM8Samples.Set should be of the form "Set ..."
	pcm.go:58:1: comment on exported method PCM8Samples.Slice should be of the form "Slice ..."
	pcm.go:63:1: comment on exported method PCM8Samples.Make should be of the form "Make ..."
	pcm.go:68:1: comment on exported method PCM8Samples.CopyTo should be of the form "CopyTo ..."
	pcm.go:95:1: comment on exported method PCM16Samples.Len should be of the form "Len ..."
	pcm.go:100:1: comment on exported method PCM16Samples.Cap should be of the form "Cap ..."
	pcm.go:105:1: comment on exported method PCM16Samples.At should be of the form "At ..."
	pcm.go:110:1: comment on exported method PCM16Samples.Set should be of the form "Set ..."
	pcm.go:115:1: comment on exported method PCM16Samples.Slice should be of the form "Slice ..."
	pcm.go:120:1: comment on exported method PCM16Samples.Make should be of the form "Make ..."
	pcm.go:125:1: comment on exported method PCM16Samples.CopyTo should be of the form "CopyTo ..."
	pcm.go:152:1: comment on exported method PCM32Samples.Len should be of the form "Len ..."
	pcm.go:157:1: comment on exported method PCM32Samples.Cap should be of the form "Cap ..."
	pcm.go:162:1: comment on exported method PCM32Samples.At should be of the form "At ..."
	pcm.go:167:1: comment on exported method PCM32Samples.Set should be of the form "Set ..."
	pcm.go:172:1: comment on exported method PCM32Samples.Slice should be of the form "Slice ..."
	pcm.go:177:1: comment on exported method PCM32Samples.Make should be of the form "Make ..."
	pcm.go:182:1: comment on exported method PCM32Samples.CopyTo should be of the form "CopyTo ..."
Fix test case to use new types.