Changing the display of intervals

[OlivierHnt]

Currently, we often display a wider interval due to the truncation of the digits up to a certain decimal.

But this leads to some very misleading results:

julia> interval(2.5) # `2.5` is exactly representable
[2.49999, 2.50001]_com

julia> interval(0.1) # `0.1` is not equal to `1//10`
[0.0999999, 0.100001]_com

I think in both cases we should be consistent with how Julia handles showing floats and display [2.5, 2.5]_com and [0.1, 0.1]_com.
If we agree on modifying this behaviour, I suppose it is technically breaking, and will have to wait for 1.0.