Move internal packages to internal subdirectory

So they can't be imported from external repositories.

I'm not giving any stability guarantees on anything except the CLI.

internal/cmd/root.go

@@ -7,8 +7,8 @@ import (
 
 	log "github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
-	generate "github.com/tweag/gomod2nix/generate"
-	schema "github.com/tweag/gomod2nix/schema"
+	generate "github.com/tweag/gomod2nix/internal/generate"
+	schema "github.com/tweag/gomod2nix/internal/schema"
 )
 
 const directoryDefault = "./"

internal/generate/generate.go

@@ -17,8 +17,8 @@ import (
 
 	"github.com/nix-community/go-nix/pkg/nar"
 	log "github.com/sirupsen/logrus"
-	"github.com/tweag/gomod2nix/lib"
-	schema "github.com/tweag/gomod2nix/schema"
+	"github.com/tweag/gomod2nix/internal/lib"
+	schema "github.com/tweag/gomod2nix/internal/schema"
 	"golang.org/x/mod/modfile"
 )
 

main.go

@@ -1,6 +1,6 @@
 package main
 
-import "github.com/tweag/gomod2nix/cmd"
+import "github.com/tweag/gomod2nix/internal/cmd"
 
 func main() {
 	cmd.Execute()