Added the what's new for iris 2.1 (#3044)

Added the what's new for iris 2.1

docs/iris/src/_templates/index.html

@@ -143,7 +143,7 @@
         <span class="linkdescr">extra information on specific technical issues</span></p>
     </li>
     <li>
-        <p class="biglink"><a class="biglink" href="whatsnew/2.0.html">What's new in Iris 2.0?</a><br/>
+        <p class="biglink"><a class="biglink" href="whatsnew/2.1.html">What's new in Iris 2.1?</a><br/>
         <span class="linkdescr">recent changes in Iris's capabilities</span></p>
     </li>
 	</ul>

docs/iris/src/whatsnew/1.5.rst

@@ -67,7 +67,7 @@ Iris 1.5 features
       plt.gca().gridlines()
       plt.show()
   
-  .. image:: pics/transverse_merc.png
+  .. image:: images/transverse_merc.png
 
 * Support for loading NAME files (gridded and trajectory data).
 * Multi-dimensional coordinate support added for

docs/iris/src/whatsnew/2.1.rst

@@ -0,0 +1,76 @@
+What's New in Iris 2.1
+**********************
+
+:Release: 2.1
+:Date: 2018-06-06
+
+This document explains the new/changed features of Iris in version 2.1
+(:doc:`older "What's New" release notes can be found here<index>`.)
+
+
+Iris 2.1 Dependency updates
+===========================
+
+* The `cf_units <https://github.com/SciTools/cf_units>`_ dependency
+  was updated to cf_units ``v2.0``.
+  cf_units v2 is almost entirely backwards compatible with v1.
+  However the ability to preserve some aliased calendars has been removed.
+  For this reason, it is possible that NetCDF load of a variable with a
+  "standard" calendar will result in a saved NetCDF of a "gregorian"
+  calendar.
+* Iris updated its time-handling functionality from the
+  `netcdf4-python <http://unidata.github.io/netcdf4-python/>`_
+  ``netcdftime`` implementation to the standalone module
+  `cftime <https://github.com/Unidata/cftime>`_.
+  cftime is entirely compatible with netcdftime, but some issues may
+  occur where users are constructing their own datetime objects.
+  In this situation, simply replacing ``netcdftime.datetime`` with
+  ``cftime.datetime`` should be sufficient.
+* Iris now requires version 2 of Matplotlib, and ``>=1.14`` of NumPy.
+  Full requirements can be seen in the `requirements <https://github.com/SciTools/iris/>`_
+  directory of the Iris' the source.
+
+Iris 2.1 Features
+=================
+
+* Added ``repr_html`` functionality to the :class:`~iris.cube.Cube` to provide
+  a rich html representation of cubes in Jupyter notebooks.
+
+  .. image:: images/notebook_repr.png
+
+* Updated :func:`iris.cube.Cube.name` to return a STASH code if the cube has
+  one and no other valid names are present. This is now consistent with the
+  summary information from :func:`iris.cube.Cube.summary`.
+* The partial collapse of multi-dimensional auxiliary coordinates is now
+  supported. Collapsed bounds span the range of the collapsed dimension(s).
+* Added new function :func:`iris.cube.CubeList.realise_data` to compute
+  multiple lazy values in a single operation, avoiding repeated re-loading of
+  data or re-calculation of expressions.
+* The methods :meth:`iris.cube.Cube.convert_units` and
+  :meth:`iris.coords.Coord.convert_units` no longer forcibly realise the cube
+  data or coordinate points/bounds. The converted values are now lazy arrays
+  if the originals were.
+* Added :meth:`iris.analysis.trajectory.interpolate` that allows you to
+  interpolate to find values along a trajectory.
+* It is now possible to add an attribute of ``missing_value`` to a cube.
+  https://github.com/SciTools/iris/issues/1588
+* Iris can now represent data on the Albers Equal Area Projection,
+  and the NetCDF loader and saver were updated to handle this.
+  https://github.com/SciTools/iris/issues/2943
+
+Bugs Fixed
+==========
+
+* All var names being written to NetCDF are now CF compliant.
+  Non alpha-numeric characters are replaced with '_', and var names now always
+  have a leading letter. https://github.com/SciTools/iris/pull/2930
+* A cube resulting from a regrid operation using the `iris.analysis.AreaWeighted`
+  regridding scheme will now have the smallest floating point data type
+  to which the source cube's data type can be safely converted using NumPy's
+  type promotion rules.
+
+Incompatible Changes
+====================
+* The deprecated :mod:`iris.experimental.um` was removed.
+  Please use consider using `mule <https://github.com/SciTools/mule>`_
+  as an alternative.

docs/iris/src/whatsnew/index.rst

@@ -9,6 +9,7 @@ Iris versions.
 .. toctree::
    :maxdepth: 2
 
+   2.1.rst
    2.0.rst
    1.13.rst
    1.12.rst