Test case: catch Throwable, not only Exception.

Test case is following:
1. bind r.s/*exception-steam* to fn collecting exception
2. run stream where user code throws j.l.Throwable
3. check if exception was collected by *exception-stream*
Catch Throwable, not only Exception.

Catching only Exception was to narrow.

User could provide code that would result in Throwable,
like: (swap a (atom {}))

That error would go unnoticed.
Merge pull request #257 from happyhacking-nl/ex-handling

Exception handling