WIP: New IJulia approach

```
In [1]:
using JuMP
m = Model()
@defVar(m, 0 <= x[1:10] <= 1)
m

Out[1]:
Minimization problem
min  0.0
Subject to 0.0 ≤ x i ≤ 1.0 ∀ i ∈ {1…10}
```
that i is an subscript too.
This will actually work for the normal console too...