debug_output_backend doesn't add newline

[Michael Marcin <mike.marcin@…>]

At least on VS2015 the debug_output_backend doesn't append a newline to the end of the log statement.

This by itself wouldn't be a problem but the other backends such as text_ostream_backend do append a newline.

This makes the log output practically unreadable.

[Andrey Semashev]

The current behavior is because different Visual Studios have different behavior - some do append a newline by themselves, some don't. There's no way the library can know this. This is why the choice is put into the user's hands - if you want a newline, you can add it in the formatter.