Cannot instantiate from `ImmutableDict`

[goerz]

I think this is a bug:

julia> Bijection(Base.ImmutableDict(1 => "hi", 2 => "bye"))
ERROR: MethodError: no method matching Base.ImmutableDict{String, Int64}(::Vector{Pair{String, Int64}})
The type `Base.ImmutableDict{String, Int64}` exists, but no method is defined for this combination of argument types when trying to construct it.

We document Bijection(dict::AbstractDict{S, T}) in Getting started, so this probably ought to work without crashing.

[goerz]

This might even be considered a bug in Julia, respectively Julia's failure to define a clear interface for AbstractDict.

In JuliaLang/julia#34297, the constructor ImmutableDict(pairs...) was added, but not ImmutableDict{K,V}(pairs...) (with type parameters), which we rely on here.

One can only hope that the implementation of other AbstractDict subtypes generally define that constructor. Any AbstractDict that does not will need a custom dict_inverse, cf #44.