Rethrow exceptions instead of throwing them again to keep their stack trace

[lefth]

When an exception is thrown again ("throw ex"), its stack will be
overwritten. Instead, it should be rethrown with its original context.

More info here (Figure 2):
https://msdn.microsoft.com/en-us/magazine/mt620018.aspx

Issue #5

[lefth]

@svermeulen Can you double check this change? I'm not sure if there's any situation where it's more advantageous to show both stack traces. In that case, we could keep the original exception as an InnerException:

throw new Exception(_exception.Message, _exception);

[svermeulen]

Makes sense. Thanks!