Create/read from hint file

[turicas]

Hint entry:

[<<Tstamp:?TSTAMPFIELD, KeySz:?KEYSIZEFIELD, TotalSz:?TOTALSIZEFIELD,
 TombInt:?TOMBSTONEFIELD_V2, Offset:?OFFSETFIELD_V2>>, Key]

Where:

• TSTAMPFIELD = 32 bits
• KEYSIZEFIELD = 16 bits
• TOTALSIZEFIELD = 32 bits
• TOMBSTONEFIELD_V2 = 1 bit
• OFFSETFIELD_V2 = 63 bits

Total = 18 bytes (HINT_RECORD_SZ).

Also: last (or first?) entry could be a file CRC (check read_crc function on bitcask_fileops.erl).