Fixed TWI buffer size parameters type.
Fixed changed HMC5883L inheritance from private to public.
Improving AT24CXX 2-Wire Serial EEPROM driver; Handle any block size.

1. read() and write() will now handle any block size. Hides page and
waiting for write to complete.
2. New functions; is_ready() and write_await() for synchronization
with device internal page write.
3. Updated example sketch with improved test case; large buffer with
multiple pages and page alignment.