OneDbf:AddField(cName,cType,nLen,nDec): public: return true
  When creating the database structure, the next field can be appended
  to the structure.

  Parameter description:
  ~~~~~~~~~~~~~~~~~~~~~~
  cName: character: no default
   database filed name

  cType: character: no default
   Field type, can be "C","M","N","D" or "L"

  nLen: numeric: default is 10,8 or 10 (after field type)

  nDec: numeric: default is 0
   Number of decimal places for type "N" or adding of length of field type
   "C" in 256 multiples. See original clipper manuals.