The Julia Base implementation of complex numbers can be found here: https://github.com/JuliaLang/julia/blob/master/base/complex.jl.

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You can work on the bonus exercises by changing `@test_skip` to `@test`.

## Bonus A
Implement the exponential function on complex numbers `exp(::ComplexNumber)`.

## Bonus B
Implement `jm` analogous to `im` so that `1 + 1jm == ComplexNumber(1, 1)`.