reorganize module

_archive/rhai_engine/rhaibook/ref/throw.md

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+Throw Exception on Error
+========================
+
+To deliberately return an error, use the `throw` keyword.
+
+```js
+if some_bad_condition_has_happened {
+    throw error;    // 'throw' any value as the exception
+}
+
+throw;              // defaults to '()'
+```
+
+
+Catch a Thrown Exception
+------------------------
+
+It is possible to _catch_ an exception, instead of having it abort the script run, via the
+[`try` ... `catch`](try-catch.md) statement common to many C-like languages.
+
+```js
+fn code_that_throws() {
+    throw 42;
+}
+
+try
+{
+    code_that_throws();
+}
+catch (err)         // 'err' captures the thrown exception value
+{
+    print(err);     // prints 42
+}
+```