Add MustNotThrow annotation

This can be added to methods to indicate they aren't allowed to throw exceptions. JBMC and related tools will
truncate any execution path on which they do with an ASSUME FALSE instruction.

Author: smowton

src/main/java/org/cprover/MustNotThrow.java

@@ -0,0 +1,3 @@
+package org.cprover;
+
+public @interface MustNotThrow { }