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_update.go

@@ -0,0 +1,22 @@
+package main
+
+import ()
+
+func commenterSessionUpdate(session string, commenterHex string) error {
+	if session == "" || commenterHex == "" {
+		return errorMissingField
+	}
+
+	statement := `
+    UPDATE commenterSessions
+    SET commenterHex=$2
+    WHERE session=$1;
+  `
+	_, err := db.Exec(statement, session, commenterHex)
+	if err != nil {
+		logger.Errorf("error updating commenterHex in commenterSessions: %v", err)
+		return errorInternal
+	}
+
+	return nil
+}