Add logical function specifications

[kgryte]

This PR

• adds specifications for logical functions.
• is derived from comparing API signatures across array libraries.

Notes

• Logical functions are widely implemented across array libraries and are used by downstream libraries.
• TensorFlow is more restrictive in requiring boolean Tensors. The current spec follows NumPy, Torch, and others in performing logical operations based on a looser definition of "truthiness".
• The proposed specifications follow the same general form as arithmetic operations, which are already present in the specification, and share the same concerns as other element-wise interfaces concerning broadcast compatibility.

[rgommers]

This is quite straightforward and no comments for over a week, I'll merge it. Thanks @kgryte