hashing is part unimplemented, part incorrect

Test:

```julia
using Test, Infinities

@testset "hash versus floating-point infinity" begin
@testset "one argument" begin
@test hash(Inf) === hash(∞)
end
@testset "two arguments" begin
for h ∈ rand(UInt, 256)
@test hash(Inf, h) === hash(∞, h)
end
end
end
```

Result:

```none
Test Summary: | Fail Error Total Time
hash versus floating-point infinity | 1 256 257 22.4s
one argument | 1 1 1.6s
two arguments | 256 256 20.9s
ERROR: Some tests did not pass: 0 passed, 1 failed, 256 errored, 0 broken.
```