try without catch should be banned

This is a serious gotcha that a style guide would do well to document (and forbid):

https://github.com/jashkenas/coffeescript/issues/3958#issuecomment-137512412

```
try 1/0
```

suppresses the exception.

I propose amending `Exceptions` to say "Do not suppress exceptions. Do not use `try` without `catch` nor `finally`, which is an undocumented and surprising way to suppress exceptions."
