Merge pull request #2 from sawilde/master

Added .NET 3.5 and Async/Await for .NET4/4.5 and portable
NEW: Add bill contracts and services
NEW: Add supplier payment contracts and service
NEW: Add version info service
NEW: category added to Invoice
NEW: costofgoods added to item invoices
NEW: payment line type added to customerpayment
Merge branch 'master' of https://github.com/MYOB-Technology/AccountRight_Live_API_.Net_SDK