Release 1.6.1

[esc24]

This PR updates the versions in init.py, setup.py and the what's new page for the 1.6.1 release. I tagged between the two commits.

[rhattersley]

Did you consider mentioning the change in PP and GRIB forecast_period handling in the "Incompatible changes" section?

[esc24]

It didn't get a mention in 1.6.0, so I didn't add it but things have change significantly now it's a bounded quantity. I'll happily take a suggestion and add it in. How about:

When a cube is loaded from PP or GRIB and it has both time and forecast period 
coordinates, and the time coordinate has bounds, the forecast period coordinate 
will now also have bounds. These bounds will be aligned with the bounds of the 
time coordinate taking into account the forecast reference time.

[rhattersley]

I like that - it's a very good start. 👍

The forecast period point has moved as well. It used to be at the end/start for PP/GRIB. Now it's in the middle to be consistent with the time point. My tweak is in bold:

When a cube is loaded from PP or GRIB and it has both time and forecast period coordinates, and the time coordinate has bounds, the forecast period coordinate will now also have bounds. These bounds will be aligned with the bounds of the time coordinate taking into account the forecast reference time. Also, the forecast period point will now be aligned with the time point.

[esc24]

I've added that into the first commit and tagged using git tag -a v1.6.1 c5099d24bbc287e8242abb7df31c0f3947bb913a -m "Iris v1.6.1 - 18 February 2014"

[esc24]

Anyone care to merge this so I can push the 1.6.1 tag up? Any objections?

[rhattersley]

Looks good. Just checking the built docs...

[rhattersley]

Anyone care to merge this so I can push the 1.6.1 tag up?

Go for it!