std.math.isPowerOfTwo: add tests and doc comment and improve assert
The assert is changed from `int != 0` to `int > 0` because negative
integers always return `false`.
Python's `math.log2` does the same and errors for 0 or negative integers.
2839e35d1cr00ster91 committed on 6/18/2023, 5:42:03 PM· committed by Andrew Kelleyparentc13ac52