Sort output of sites (#185)

* sort output of sites(::Quantum) so sites are in order

* formatting

* use sort! to save nanobyte allocations

src/Quantum.jl

@@ -108,7 +108,7 @@ Returns the sites of a [`Quantum`](@ref) Tensor Network.
 """
 function sites(tn::Quantum; kwargs...)
     if isempty(kwargs)
-        collect(keys(tn.sites))
+        sort!(collect(keys(tn.sites)))
     elseif keys(kwargs) === (:at,)
         findfirst(i -> i === kwargs[:at], tn.sites)
     else