An exercise on using PayPal Express Checkout API
###The express checkout flow is implemented in the following order or files:
- index.php - product page
- expresscheckout.php - redirect to PayPal for payment
- review.php - reviewing and confirming order
- order_confirm.php - order confirmed
###The remaining files are for support:
- header.php, footer.php - html templating
- paypalfunctions.php - wraps Paypal Express Checkout API