internal/cmd/qgo: port qgo from loader to packages

exclude ReplaceAll, for now

Change-Id: I2574bbbb3e1d72b64770fdee759c2d68b272902c
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2322
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/pkg/math/math.go b/pkg/math/math.go
index c20e405..a66f27a 100644
--- a/pkg/math/math.go
+++ b/pkg/math/math.go
@@ -446,7 +446,7 @@
 	return math.Remainder(x, y)
 }
 
-// Signbit returns true if x is negative or negative zero.
+// Signbit reports whether x is negative or negative zero.
 func Signbit(x float64) bool {
 	return math.Signbit(x)
 }