Document in behaviour

[dpsanders]

julia> 3.5 ∈ interval(3, 4)
false

This should either work or give me an error message telling me that this is not supported for intervals and telling me which special interval function to use instead (which is not discoverable).

[dpsanders]

Apparently it's in_interval

[OlivierHnt]

I took the freedom of re-naming this issue since this behaviour is intentional and has been extensively discussed. In a nutshell, in Julia the function in pertains to containers (which Interval is not); we cannot remove it completely (throw an error) for otherwise some generic functions fail, we cannot overload it with our own definition since this leads to silent errors in generic code.

We should highlight this in the docs, and maybe just add a docstring for in?