[FeatureRequest] Show the type of an exception in the stacktrace, when one occurs
Heyho everybody,

I am building a normal REST-API with Prologue, norm and jsony, the database being sqlite.

Recently found myself in a scenario where I wanted to configure some HTTP404 responses.
So I first wanted to see what currently happens if I throw a request for a resource at the server that I know doesn't exist. Easily said and done, it causes an error from the database, which leads to the default HTTP500 response in Debug mode being shown.

```
ERROR Record not found
Async traceback:
  /home/isofruit/dev/nimstoryfont/src/nimstoryfont.nim(18)                                        nimstoryfont
  /home/isofruit/dev/nimstoryfont/src/nimstoryfont.nim(15)                                        main
  /home/isofruit/.nimble/pkgs/prologue-0.5.0/prologue/core/application.nim(533)                   run
  /home/isofruit/.nimble/pkgs/prologue-0.5.0/prologue/core/beast/server.nim(31)                   serve

  [... just a very long stacktrace ...]

    /home/isofruit/.choosenim/toolchains/nim-1.6.2/lib/pure/asyncmacro.nim(31)                      switchNimAsyncContinue
    /home/isofruit/.choosenim/toolchains/nim-1.6.2/lib/pure/asyncmacro.nim(131)                     switchIter
    /home/isofruit/.choosenim/toolchains/nim-1.6.2/lib/pure/asyncfutures.nim(389)                   read
  ]#
Exception message: Record not found

DEBUG 500 Internal Server Error {"content-type": @["text/plain; charset=UTF-8"]}
```

What I wanted to do from there then, is wrap a try-catch around the database request in my controller and if I catch an exception of the type that is thrown when there is no record, then I want to return an HTTP404. 

Since the stack trace that is shown when an error occurs doesn't include the *type* of the Exception that was thrown though, I had to write the code that catches the exception and echo's out its type myself and then trigger the scenario that caused the exception.

```nim
  try:
        <some database calling code>
            
    except CatchableError as e:
        echo "Error of type '" & $e.name & "'"
        raise e
```

To reduce that hassle in the future, it would be a really nice convenience feature if we could have the type of an exception show up in the stacktrace that is printed to the console. That way it's easier to see what to catch in a `try-except` block.