Conjugate of operators

[vtorggler]

The conjugate of operators
conj(H)
does not have an effect. It also does not give an error. I think this is dangerous.

In other words,
conj(H).data == conj(H.data)
it not necessarily true.

[david-pl]

This actually has nothing to do with QuantumOptics, but it's a Julia issue. There is a method defined for conj in Base.operators which is just

conj(x) = x

so it works for literally anything,

julia> conj("anything")
"anything"

However, this is already fixed (see JuliaLang/julia#26288), so once v0.7 is released, it won't be a problem anymore.

[david-pl]

The latest commit implements a method of conj for dense and sparse operators, and otherwise throws an error message.