exception translators considered even for types deriving from std::exception, now

- also added docs for exception translators
- updated approvals

docs/tostring.md

@@ -55,6 +55,16 @@ namespace Catch {
 }
 ```
 
+## Exceptions
+
+By default all exceptions deriving from `std::exception` will be translated to strings by calling the `what()` method. For exception types that do not derive from `std::exception` - or if `what()` does not return a suitable string - use `CATCH_TRANSLATE_EXCEPTION`. This defines a function that takes your exception type, by reference, and returns a string. It can appear anywhere in the code - it doesn't have to be in the same translation unit. For example:
+
+```
+CATCH_TRANSLATE_EXCEPTION( MyType& ex ) {
+	return ex.message();
+}
+```
+
 ---
 
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