Beacon spec updates based on feedback:
- Beacon method is renamed to sendBeacon
- sendBeacon is on navigator, not window
- url parameter comes first, method parameter is optional with "GET" default action
- cross-origin transmissions cannot use "PUT" method
- Added details on UA "best effort" attempts
- Data transmission is limited to 10KBs.
- Updated errors to URLMismatchError, SecurityError, QuotaExceededError
- Updated Processing Model to match spec behavior
- Updated abstract to remove "user agent taking the responsibility to eventually send the data"
- Updated Ack section