Do a large chunk of the move to go

This commit moves a huge chunk of the code to go. The TODO.md document
indicates what is left to be done.

internal/fsx/type.go

@@ -0,0 +1,13 @@
+package fsx
+
+import "os"
+
+func IsDirectory(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && info.Mode().IsDir()
+}
+
+func IsFile(path string) bool {
+	info, err := os.Stat(path)
+	return err == nil && info.Mode().IsRegular()
+}