Use Int for ID instead of string

[SimonDanisch]

Observables.jl/src/Observables.jl

Line 20 in 40243b2

id::String

Should give quite a speed up compared to a string field - also it will be much clearer that it's an ID.
I also don't like to mix names and ids like this. It should either be a name or a unique id in my book ;)
We could have something like this, to have the best of both worlds:

const name_dict = Dict{Int, String}()
Observable(x, name = nothing) = (...; name != nothing && name_dict[id] = name)
name(x::Observable) = get(name_dict, x.id) do 
    error("Observable doesn't have a name. You may call it numer: $(x.id), though")
end

Could do a PR if this is appreciated

[SimonDanisch]

Should I go ahead and implement this?

[twavv]

I believe that you did this in #40. :^)