MAINT: Change spectral to nipy_spectral, update docs, leave aliases

[endolith]

For #879, rename spectral to nipy_spectral (to distinguish from Spectral). Leave spectral as an alias, and spectral() as a shortcut, but only in footnotes.

[endolith]

Check my docstring formatting. I used

:func:`spectral`

and

 `set_cmap('nipy_spectral')`

for instance. not sure if that's right for functions

[WeatherGod]

I think you need double backquotes for the set_cmap call example, but that is completely from memory.

[dmcdougall]

I know it's only aesthetic, but it wouldn't hurt to have all the data line up nicely.

[endolith]

Oh I was thinking of refactoring the datad assignments into a single dictionary too. These sorts of OCD formatting are welcome? :)

[dmcdougall]

Personally, if it makes the code more readable then that's preferred. Ideally, @WeatherGod will weigh in with his PEP8 ninja chops :)

[endolith]

Well PEP8 says not to align code for readability, but I think common usage disagrees. http://www.python.org/dev/peps/pep-0008/#pet-peeves

[endolith]

anything else that needs to be done here?

[pelson]

@NelleV - your feedback on this would be highly valuable if you have a moment?

[NelleV]

LGTM 👍