'Adds a dimension to the Dimension section of the NetCDF data structure.
Note that this function merely adds a new dimension that the variables can
reference.  The values for the dimension, if desired, should be added as
a variable using `createVariable`, referring to this dimension.
Parameters
name : str
Name of the dimension (Eg, \'lat\' or \'time\').
length : int
Length of the dimension.
See Also
createVariable'

def createDimension(self, name, length):

    if ((length is None) and self._dims):
        raise ValueError('Only    first    dimension    may    be    unlimited!')
    self.dimensions[name] = length
    self._dims.append(name)
