Rename "String" type to "OptString"

internal/lvgen/gen/main.go

@@ -22,7 +22,6 @@ import (
 	"github.com/digitalocean/go-libvirt/internal/lvgen"
 )
 
-// TODO: make these an argument
 const protoPath = "src/remote/remote_protocol.x"
 
 func main() {

internal/lvgen/generate.go

@@ -82,6 +82,10 @@ var goEquivTypes = map[string]string{
 	// requires us to ditch the typedef that would otherwise be generated.
 	"NonnullString": "string",
 
+	// remote_string gets renamed "String" by the generator, so here we'll
+	// rename that to OptString - these are optional strings, and can be "null".
+	"String": "OptString",
+
 	// TODO: Get rid of these. They're only needed because we lose information
 	// that the parser has (the parser knows it has emitted a go type), and then
 	// we capitalize types to make them public.