Idea/feature-request: Line-brek/new-line decorators?

[Lord-Kamina]

I've recently found myself adding new-line decorators to make formatting of multi-line debug messages easier on the eyes.

I'm using the following pattern:

	inline static const std::string newLineDec = "             └---"; // new line decorator.

In this case the number of spaces is arbitrary and accounts for the formatting I'm using for the timestamp.

So then, for a large message I'll do something like the following:

		std::string logmsg{fmt::format(
		"Found system paths:\n"
		"{8}base:          {0}\n"
		"{8}share:         {1}\n"
		"{8}locale:        {2}\n"
		"{8}sysConf:       {3}\n"
		"{8}home           {4}\n"
		"{8}config:        {5}\n"
		"{8}data:          {6}\n"
		"{8}cache:         {7}",
		base, share, locale, sysConf, home, conf, data, cache, SpdLogger::newLineDec
		)};

And it looks pretty nice, like so:

Would it be feasible to have such a thing as a built-in option in spdlog, such that it (optionally) detects line-breaks automatically and appends a configurable string such as what I'm using?

[tt4g]

I think this could be achieved by parsing the log messages using a custom flag formatter.
See https://github.com/gabime/spdlog/wiki/Custom-formatting#extending-spdlog-with-your-own-flags