Add form validation (bug 929072)
Merge pull request #17 from kumar303/forms

Add form validation (bug 929072)
general docs
Enforce duplicate external IDs for products
Fix status for created seller
Fix redundant seller_id, slim down pay_method
Remove unnecessary signing key ID
Document seller, product, trans, notice APIs
Merge pull request #20 from kumar303/docs

Documented a bunch of APIs
Add buttons styling (bug 931061)