Add crashes and fixes found during fuzzy testing

* Let unhandled exceptions propogate to user
 * Report eval_error when break statement is not in loop
 * Fix handling of 0 length scripts closes #193
 * Don't crash on arity mismatch - Specifically affects the case where no overloads exist for a given function
 * Fix error printing for `bind` calls
 * Handle unexpected continue statement
 * Check arity during bind
 * Don't allow arith conversion on variadic function
 * Correct `bind` parameter match count
 * Add in expected Boxed_Value exception cases
 * Check access to AST, don't allow `;` in func def
 * Don't attempt arithmetic unary & call
 * Don't crash on 0 param call to `bind`
 * Catch errors during member function dispatch
 * Properly handle type of const bool &

include/chaiscript/language/chaiscript_common.hpp

@@ -276,10 +276,13 @@ namespace chaiscript
       template<typename T>
         static std::string format_location(const T &t)
         {
-          std::ostringstream oss;
-          oss << "(" << t->filename() << " " << t->start().line << ", " << t->start().column << ")"; 
-
-          return oss.str();
+          if (t) {
+            std::ostringstream oss;
+            oss << "(" << t->filename() << " " << t->start().line << ", " << t->start().column << ")"; 
+            return oss.str();
+          } else {
+            return "(internal)";
+          }
 
         }