is the same as an arg matrix. LGTM=crawshaw R=crawshaw CC=golang-codereviews https://golang.org/cl/152850043
Also fix String methods' receivers to be T, not *T, so that var m f32.Mat32 s := fmt.Sprintf("m=%v", m) works. LGTM=crawshaw R=crawshaw CC=golang-codereviews https://golang.org/cl/147490043
LGTM=crawshaw R=crawshaw CC=golang-codereviews https://golang.org/cl/150380043