Style and API change in ebv()

[weaverba137]

The method desiutil.dust._Hemisphere.ebv(self, l, b, interpolate) triggers style warnings since l is considered a potentially ambiguous variable name. The suggested replacements are gal_l and gal_b, which are both more informative and unambiguous. However, since it is possible in principle that .ebv() is called with .ebv(l=..., b=..., ...), this is a potential API breaking change, so this should be applied to a future desiutil 4.0.

[weaverba137]

I did a search for calls of .ebv(). I found no instances where .ebv() is called with l and b set as keywords. Furthermore, the .ebv() method that is proposed to be changed is actually wrapped by other .ebv() methods and/or the desiutil.dust.ebv() function.