Write sav files

[JanMarvin]

• vtype needs to be expanded to add some -1 for strings longer than 8 chars
• names need to be expanded for >255 chars will require longnames handling
• var.labels implementation
• missings need handling kinda work already. could provide a missing table, though not sure if really required or beneficial
• value labels need handling
• long value labels need handling they are not long labels, just labels for long strings. nothing useful for the R world

[JanMarvin]

• compress = 1
  • handle val_b and doubles in chunks and store them in a fashion similar to SPSS
  • handle splitted character variables
  • handle buf_s similar to buf_d
  • improve this spaghetti code?
• handle strings longer than 255 characters