Attachments upload support
README formatting tweak
Fix attachments example
Fix another error in attachments example
Generic algorithm for GUID detection
Add BankTransactions and BankTransfers
Add objects to README
Fix the GUID filtering

Any parameter ending in ID is assumed to be a Guid (which is correct
against current Xero API docs)
Filter output now correct
Wrong test fixed
Full Attachments API

Note: Changed parameter order for put_attachment
Bug fix
Merge pull request #42 from wegotpop/master

Implement the Attachments API.