Add a simple regression test for fixed-point checking

testcases/regression/certificate_AdditionSimple_Fixed.v

+Require Import Flover.CertificateChecker.
+Definition C12 :expr Q := Const (F 32 22) ((1657)#(5)).
+Definition u0 :expr Q := Var Q 0.
+Definition e3 :expr Q := Binop Plus C12 u0.
+Definition Rete3 := Ret e3.
+
+
+Definition defVars_additionSimple :(nat -> option mType) := fun n =>
+if n =? 0 then Some (F 32 24) else None.
+Definition thePrecondition_additionSimple:precond := fun (n:nat) =>
+if n =? 0 then ( (-100)#(1), (100)#(1)) else (0#1,0#1).
+
+Definition absenv_additionSimple :analysisResult := Eval compute in
+FloverMap.add e3 (( (1157)#(5), (2157)#(5)), (9)#(16777216)) (FloverMap.add u0 (( (-100)#(1), (100)#(1)), (1)#(16777216)) (FloverMap.add C12 (( (1657)#(5), (1657)#(5)), (1)#(4194304)) (FloverMap.empty (intv * error)))).
+
+Theorem ErrorBound_additionSimple_Sound :
+CertificateCheckerCmd Rete3 absenv_additionSimple thePrecondition_additionSimple defVars_additionSimple = true.
+Proof.
+  vm_compute; auto.
+Qed.