Updated documentation to note the pow(0, 0) case.

[meltinglava]

Ref #78

[hauleth]

Quoting prof Knuth:

On the other hand, Cauchy had good reason to consider 0^0 as an undefined limiting form, in the sense that the limiting value of f(x)^g(x) is not known a priori when f(x) and g(x) approach 0 independently. In this much stronger sense, the value of 0^0 is less defined than, say, the value of 0 + 0. Both Cauchy and Libri were right, but Libri and his defenders did not understand why truth was on their side.

https://arxiv.org/abs/math/9205211

[cuviper]

@hauleth It's not clear to me if you're quoting that in favor or against, or just representing the debate.

Anyway, commenting the existing behavior is harmless.

bors r+

[bors[bot]]

Build succeeded

• continuous-integration/travis-ci/push

[hauleth]

@cuviper my comment was in favour of current behaviour as I think it is more reasonable solution in case of computation. pow(0, 0) is "mathematically undefined" when we are working in area of mathematical analysis, and in such case num crate isn't that much helpful. We could quote this paper as a reasoning for current behaviour and why we think it is acceptable for us.