This change loads the full symbol table when we open a persisted block
and allocates a string for each. This ensures that strings retrieved
through the index can be used after the block was closed.
Before we backed the strings by the mmap'd byte regions which would
segfault in this case.
Also remove an inconsistency in the disk format and move both offset
tables to the end (breaking change).
When decoding data from mmaped blocks, we would like to retrieve
a string backed by the mmaped region. As the underlying byte slice
never changes, this is safe.
* Expose Stone as it is used in an exported method.
* Move from tombstoneReader to []Stone for the same reason as above.
* Make WAL reading a little cleaner.
Signed-off-by: Goutham Veeramachaneni <cs14btech11014@iith.ac.in>
