Update to 3.3.18
    
    - New upstream release 3.3.18
      - minor bug fixes for corner cases
      - assembler fixes for x86_64
      - preliminary support for variable length records in FST files
      - added fstUtilityBinToEsc and fstUtilityEscToBin for conversion of binary
        data to C-style strings
      - allow escaped strings in VCD files to encode a richer set of data for
        non-standard "s" VCD records
      - to comply with fst2vcd, vcd readers now handle "string" variable type
        keyword
      - add detection for Verilog XL-style VCD identifiers in all VCD loaders in
        gtkwave in order to aid in indexing
      - more warnings fixes
      - fix mif_draw_string so it does not emit escaped character codes