blas: fix documentation of Use functions

This was noticed while adapting JuliaLang/Microbenchmarks#27 to the new
Gonum import paths.
This CL somewhat clarifies the correct default implementation (pure-Go)
used by the various blas{32,64} and cblas{64,128} packages.

blas/blas32/blas32.go

@@ -12,7 +12,8 @@ import (
 var blas32 blas.Float32 = gonum.Implementation{}
 
 // Use sets the BLAS float32 implementation to be used by subsequent BLAS calls.
-// The default implementation is native.Implementation.
+// The default implementation is
+// gonum.org/v1/gonum/blas/gonum.Implementation.
 func Use(b blas.Float32) {
 	blas32 = b
 }

blas/blas64/blas64.go

@@ -12,7 +12,8 @@ import (
 var blas64 blas.Float64 = gonum.Implementation{}
 
 // Use sets the BLAS float64 implementation to be used by subsequent BLAS calls.
-// The default implementation is native.Implementation.
+// The default implementation is
+// gonum.org/v1/gonum/blas/gonum.Implementation.
 func Use(b blas.Float64) {
 	blas64 = b
 }

blas/cblas128/cblas128.go

@@ -12,7 +12,8 @@ import (
 var cblas128 blas.Complex128 = gonum.Implementation{}
 
 // Use sets the BLAS complex128 implementation to be used by subsequent BLAS calls.
-// The default implementation is cgo.Implementation.
+// The default implementation is
+// gonum.org/v1/gonum/blas/gonum.Implementation.
 func Use(b blas.Complex128) {
 	cblas128 = b
 }

blas/cblas64/cblas64.go

@@ -12,7 +12,8 @@ import (
 var cblas64 blas.Complex64 = gonum.Implementation{}
 
 // Use sets the BLAS complex64 implementation to be used by subsequent BLAS calls.
-// The default implementation is cgo.Implementation.
+// The default implementation is
+// gonum.org/v1/gonum/blas/gonum.Implementation.
 func Use(b blas.Complex64) {
 	cblas64 = b
 }