[Release] SunPy v0.7.8

[Nabil Freij]

Dear all,

I have taken over.

More importantly, we see a bug fix release of SunPy. I would recommend upgrading as it fixes the important issue that the new version of Pandas (v0.20.1) breaks SunPy which we have fixed.

Changelog:

0.7.8
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* The SunPy data directory "~/sunpy" is no longer created until it is used (issue #2018)
* Change the default representation for the Heliographic Carrington frame so Longitude follows the convention of going from 0-360 degrees.
* Fix for surface gravity unit.
* Support for Pandas 0.20.1

0.7.7
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* Fix errors with Numpy 1.12

Please enjoy,

The Sunpy Developers