Added Billed for time_entry
Updated client API
Updated estimates
Updated API for invoices
Added ability to query Languages (from API)
Updated API for payments, including gateway_transactions
Added Gateway lookup (as per API)
Added hour_budget and budget to Project API
Added skipping of deprecated values 
(to prevent workarounds for deprecated values)
Updated API for recurring.
Added Staff.current call (as it's in the API)
Added System API calls
Added Tax API
Attempt to make README cleaner
updated history
add simple error_msg attribute to actions: create, update