#101 Create temporary chunks when writing

[J. Scott Edwards]

Change so that when writing data, instead of modifying an existing chunk, write into a new chunk and then if the program aborts for any reason before it is finished it will be the way it was before.

[J. Scott Edwards]

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Here's another idea: keep two copies of the chunk_info_table and use it to restore back to the previous copies of the chunks even after the program has finished?

[J. Scott Edwards]

This also solves the backup problem because we don't have to sort the diff file, just diff the old chunks with the new chunks to create the .dif file.