add TRBDF2 as DIRK

Author: MarcoArtiano

examples/trixi_dirk.jl

@@ -29,7 +29,8 @@ sol = solve(
     # Implicit.RKImplicitEuler();
     # Implicit.KS22();
     # Implicit.C23();
-    Implicit.L33();
+    # Implicit.L33();
+      Implicit.RKTRBDF2();
     dt = 1.0, # solve needs some value here but it will be overwritten by the stepsize_callback
 	ode_default_options()..., callback = callbacks,
 	# verbose=1,