fix: allow imported binary variables to be set (#85)

Change the way imported binary variables are imported, from
`reflect.ValueOf(val)` to `reflect.ValueOf(&val).Elem()`, to allow these
variables to be set from the interpreter.
Regenerate stdlib packages accordingly.
Ensure that binary value is forwarded if it exists.
Add tests.

_test/assign0.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+)
+
+func main() {
+	http.DefaultClient.Timeout = time.Second * 10
+	fmt.Println(http.DefaultClient)
+	http.DefaultClient = &http.Client{}
+	fmt.Println(http.DefaultClient)
+}
+
+// Output:
+// &{<nil> <nil> <nil> 10s}
+// &{<nil> <nil> <nil> 0s}