Iris 2.3 What's New (SciTools#3450)

* Manual elements of What's New

* renamed manual 2.3 What's New entries

* Created 2.3 What's New document.

* Referencing 2.3 What's New in index.html

* Explicit reference to 2.3.0

* Added separator underneath showcases

* Deleted contributions folder.

* Referenced CF conventions for NetCDF format example

* Moved CF 1.7 support from bugfix to new feature.

* Typo in Cube.collapsed.

* Underlines, code-block language and CF terminology fixes.

* Correction to climatological docstring and What's New.

* Correction to climatological docstring and What's New.

* Added Geostationary projection to CF 1.7 showcase.

* Chunking strategy phrasing.

* CubeList link for render HTML point.

* Removed reference to latest.rst from What's New index.

* CF 1.7 section links.

* Removed duplicate note about realisation with iris.analysis.RMS

* Improved formatting for cube equality point.

* Fixed Dask dependency to by >=1.2.

* Proj4 dependency phrasing.

* with masked arrays -> with arrays with missing points.

* var_name name token phrasing.

* Removed reference to private method Cube._html_repr_.

* abf/abl cube pluralisation.

* Link for NEMO example.

* Corrected internal documentation links.

* Corrected *integer* value support.

* Geostationary includes load and save support.

* Clarified self-referencing NetCDF variables.

* Reworded CF 1.7 showcase.

* Internal address fixes.

* Removed name tokens from the CF 1.7 showcase.

Dask landsea masks bugfix (SciTools#3255)

* Fix landsea-mask data access for UM files.

* Review changes.

* Fixed some stale comments  + unused variables.

Merge pull request SciTools#3198 from dkillick/version_string_v2.2.0

Update version string to v2.2.0

Updated to v2.1.0. (SciTools#3051)

v2.0.0

http://scitools.org.uk/iris/docs/v2.0/whatsnew/2.0.html

Converted the contributions into the whatsnew.

Merge pull request SciTools#2562 from lbdreyer/bump_version

Bump version to 1.13.0

Merge pull request SciTools#2332 from bjlittle/docs-template-copyrigh…

…t-year

Update template copyright year end

Release 1.12.0rc1 definition. (SciTools#2296)

* Release 1.12.0rc1 definition.

1.12.0rc0 version string