Your baby is due in two weeks. Naturally, I'm over the moon about this, but I'm also feeling a bit sentimental . . . hence this letter.   So here I am at the kitchen table, thinking about you and Anna and how your world's about to change. You'll make a terrific father.    But it won't be easy.    There'll be days when you'll question your sanity. Evenings when you just want to shut yourself in your bedroom. Without Anna; without your boy. And one morning you'll wake up and realize that you no longer know who you actually are. Who you used to be before you became a stressed-out parent.