v0.2.1
  - Add reciprocal_coordinates and reciprocal_increment methods to the dimension
    object.
  - Added fft function to the csdm object.
  - Added transpose method to the csdm object.

v0.2.0
 - Fixed a bug in cp.plot method.
 - Added following methods.
   - __eq__ for all class
   - __add__ = Adds two for csdm object.
   - __iadd__ = Adds two csdm objects in place.
   - __sub__ = Subtrace two csdm objects.
   - __isub__ = Subtrace two csdm objects in place.
   - __mul__ = Multiply the components of the csdm object by a scalar.
   - __imul__ = Multiply the components of the csdm object by a scalar in place.
   - __truvdiv__ = Divide the components of the csdm object by a scalar.
   - __itruediv__ = Divide the components of the csdm object by a scalar in place.
   - split = Split the dependent-variables into individual csdm objects.

  - Numpy dimension reduction functions
   - sum = Sum along a given dimension.
   - prod = Product along a given dimension.

 - Numpy ufunc functions
   - sin, cos, tan, arcsin, arccos, arctan, sinh, cosh, tanh, arcsinh, arccosh, arctanh
   - exp, exp2, log, log2, log10. expm1, log1p, negative, positive, absolute, fabs, rint
   - sign, conj, conjugate.
   - sqrt, square, cbrt, reciprocal

 - Added apodization functions.
   - sin, cos, tan, arcsin, arccos, arctan, exp

v0.1.5
 - Added method to convert the frequency dimension to nmr dimensionless frequency ratio.
 - csdmpy.plot method also displays the dimension index on the axis label.

v0.1.4
 - Added to_dict method to the CSDM, Dimension, and DependentVariable objects. Return the said object as python dictionary.

version 0.1.3
 - Fixed warning message when physical quantity name is not found in the astropy units package.
 - Added dumps and loads function to dump and load the data model as json serialized string, respectively
   without serializing it to a file.

version 0.1.2
 - Add a required `unsigned_interger_type` for SparseSampling dimension.
 - Fixed minor bugs.

version0.0.12
 - Added a tags attribute to the CSDmodel object.
 - Changed 'sampling_interval' key to 'count'.
 - Changed 'quantity' key to 'quantity_name'.
 - Changed 'index_zero_value' key to 'coordinates_offset'.
 - Changed 'fft_output_order' key to 'complex_fft'.

version0.0.11
- Renamed IndependentVariable class to Dimension.
- Renamed LinearlySpacedDimension class to LinearDimension.
- Renamed ArbitrarilySpacedDimension class to MonotonicDimension.

- Added a reciprocal attribute to LinearDimension and MonotonicDimension classes.
- Removed the reverse attribute from all Dimension classes.

- Changed 'sampling_interval' keyword to 'increment'.
- Changed 'reference_offset' keyword to 'index_zero_value'.
- Changed 'linear_spacing' literal to 'linear'.
- Changed 'arbitrarily_sampled' literal to 'monotonic'.
- Changed the defining of the coordinates from LinearDimension to
        $X^(ref) = m_k J_k - c_k 1$
  to
        $X^(ref) = m_k J_k + c_k 1$,
  where $c_k$ is the reference offset, $m_k$ is the increment, and $J_k$ is the
  set of integer indices along the dimension.

- Added 'description' key to 'Dimension', 'DependentVariable' and 'CSDM' object.
- Changed 'CSDM' keyword to 'csdm'
- Changed 'FFT_output_order' keyword to 'fft_output_order'
- Changed 'components_URL' keyword to 'components_url'

New methods

- sum(index=0) Sum of data values from the dependent variable along the
        independent variable at indices given by `index`.
- prop(index=0) Product of data values from the dependent variable along the
        independent variable at indices given by `index`.
