Add more VS debug visualizers

[Reedbeta]

Hello! I've added debug visualizers for toml::table, toml::array, and the parse_result and parse_error types that show up when using the non-exceptions build of the library. These mainly just cut down on visual clutter in the watch window.

Here's what a table looks like with the new visualizers:

For comparison, this is what it looked like before:

This is what parse_result looks like with a successful parse:

And this is what it looks like with an error:

Hope this is useful to others!

[marzer]

Oh, fantastic! I was planning on doing this eventually, but debugging natvis is such a PITA... very happy for someone to have done that for me, so thanks :)

[Reedbeta]

Thanks, happy to help! Natvis is a lot easier now that you can turn on its diagnostic messages and live-edit it during a debugging session. :)

[marzer]

also, TIL you can reinterpret_cast<> in natvis