Hide bare constructors and remove copy(::Langevin)

src/Integrators.jl

@@ -19,15 +19,13 @@ mutable struct Langevin
     Δt  :: Float64
     λ   :: Float64
     kT  :: Float64
-end
 
-function Langevin(Δt; λ, kT)
-    Δt <= 0 && error("Select positive Δt")
-    return Langevin(Δt, λ, kT)
+    function Langevin(Δt; λ, kT)
+        Δt <= 0 && error("Select positive Δt")
+        return new(Δt, λ, kT)
+    end    
 end
 
-Base.copy(dyn::Langevin) = Langevin(dyn.Δt, dyn.λ, dyn.kT)
-
 """
     ImplicitMidpoint(Δt::Float64; atol=1e-12) where N
 
@@ -42,15 +40,14 @@ periods of simulation time.
 mutable struct ImplicitMidpoint
     Δt   :: Float64
     atol :: Float64
-end
 
-function ImplicitMidpoint(Δt; atol=1e-12)
-    Δt <= 0 && error("Select positive Δt")
-    return ImplicitMidpoint(Δt, atol)
+    function ImplicitMidpoint(Δt; atol=1e-12)
+        Δt <= 0 && error("Select positive Δt")
+        return new(Δt, atol)
+    end    
 end
 
 
-
 ################################################################################
 # Dipole integration
 ################################################################################