api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/commenter_session_get.go

@@ -0,0 +1,25 @@
+package main
+
+import ()
+
+func commenterSessionGet(session string) (commenterSession, error) {
+	if session == "" {
+		return commenterSession{}, errorMissingField
+	}
+
+	statement := `
+    SELECT commenterHex, creationDate
+    FROM commenterSessions
+    WHERE session=$1;
+  `
+	row := db.QueryRow(statement, session)
+
+	cs := commenterSession{}
+	if err := row.Scan(&cs.CommenterHex, &cs.CreationDate); err != nil {
+		return commenterSession{}, errorNoSuchSession
+	}
+
+	cs.Session = session
+
+	return cs, nil
+}