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Seek to a position in the file.
uint64_t seek( int64_t offset, file_base::seek_basis whence);
This function updates the current position in the file.
                  The requested position in the file, relative to whence.
                
                  One of seek_set,
                  seek_cur or seek_end.
                
The new position relative to the beginning of the file.
Thrown on failure.