Generate an SHA256 hexdigest for the content and not the timestamp

[gridhead]

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This has not been mentioned of before.

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#72, once merged will bring this problem to point. Hashing the contents would help notice the differences between two nearly identical files while hashing the timestamp does not add much value as it is already added in the name. Also, the inclusion of the hexdigest string in the file name can make it too long and render it invalid on some file systems. It should clearly be stored only in the contents of an SWD.