Table sort with a tuple of keys - #4671

+1 to allowing any iterable

@astrofrog - I changed the test to allow any iterable, the same as Table.argsort.

Appveyor failed to install conda, restarting the build.

Up, @astrofrog @taldcroft ?
Seems straightforward ;)

Needs a change log -- perhaps under "new feature" for 1.2?

@saimn - you should update the doc strings for sort and argsort to indicate that key can be a string, list or tuple. But for instance a numpy array of column names doesn't work.

In theory one could make the input side a bit more tolerant by doing key = list(key) after the check for key being a string. That's your call, I'm never sure how far to go with allowing any kind of sequence as an input (including e.g. a dict) since that might mask a bug in the calling code.

@taldcroft - About the docstring, it seems redundant to specify 'tuple of str'. The current 'str or list of str' seems enough to me.
Otherwise I agree with you it is sometimes difficult to know where to put the limits (i.e. should we try to convert to list ?), the important being to be consistent, and to follow common usages: in this case tuple and list are very similar, numpy.sort allows both (and its docstring mentions only 'str or list of str') but not ndarray, Table.argsort rely on Table.__getitem__ which will allow only tuple and list. So I would stay with the current changes, which seems to be the good compromise.

Added changelog in 1.2 as suggested by @pllim

@saimn - fair enough. Thanks!