SONSetTextMarkChan

  SONSETTEXTMARKCHAN creates a TEXTMARK channel
              FH = SON file handle
              CHAN = the channel number for the new channel
              SPHYCH = the physical channel number
              BUFSIZE = the size of the internal buffer (up to 32768 bytes)
              COMMENT = channel comment string
              CHANTITLE = channel title string
              RATE = the expected data rate (during sampling)
              UNITS = channel units string
              POINTS = maximum number of characters per marker

  Returns zero or a negagtive error

  Author:Malcolm Lidierth
  Matlab SON library:
  Copyright © The Author & King's College London 2005-2006