Dbf:AddField(cName,cType,nLen,nDec): public: return true
  The last created object OneDbf is appended with next field.

  Parameter desription:
  ~~~~~~~~~~~~~~~~~~~~~~~
  cName: character: no default
   new database field name

  cType: character: no default
   Database field type, could be "C","M","N","D" or "L


  nLen: numeric: default is 10,8 or 1 (after field type)
   Database field size.

  nDec: numeric: default is 0
   It is number of decimal digits for "N" type, or adding the width
   of type "C" in multiples of 256. (see the clipper manuals)