NTVtype extension

• issues

  • bugs #27 #28 #30
  • enhancement #29 #31

• NTV Structure

  • add NTVtype extension (class TypeBase / Datatype)
  • add attributes in global Namespace (#29, #31)

• documentation

  • add NTVtype : narray, ndarray, unit, xndarray, xdataset
  • new version of NTV-tab Internet Draft (Version 01)
  • new Internet Draft: NTV-schema