Display zero Complex{Bool} as false*im

[jishnub]

Since

julia> Complex(false,false) === false*im
true

we may use the latter form, which is more concise. This makes the display of structured matrices easier to read.
On master:

julia> Diagonal(fill(im, 2))
2×2 Diagonal{Complex{Bool}, Vector{Complex{Bool}}}:
                   im           ⋅          
          ⋅                              im

This PR

julia> Diagonal(fill(im, 2))
2×2 Diagonal{Complex{Bool}, Vector{Complex{Bool}}}:
       im     ⋅    
    ⋅            im

[KristofferC]

2×2 Matrix{Complex{Bool}}:
                   im  Complex(false,false)
 Complex(false,false)                    im

looks kind of strange to me I must say

[simeonschaub]

In case the eltype is concrete, we could just print this as 0

[StefanKarpinski]

Agree, if the eltype is concrete as in these examples, print Complex(1, 0) as 1 + 0im, Complex(0, 0) as 0 + 0im, Complex(0, 1) as 0 + 1im and so on. If we don't have precise type information then we're in "scalar context" and I think printing as Complex{Bool}(0, 0) and so on might be clearer.