Add support for tripple quote render

[tibcoplord]

On parse hocon supports tripple quotes for multi-line strings :

myitem = """line1
line2"""

However when this is rendered it becomes :

myitem = "line1\nline2"

It would be great if the render can ( perhaps optionally ) use tripple quoting as well.

[havocp]

There is a separate feature (ConfigDocument) that attempts to round trip formatting. Config doesn't know the original formatting so it wouldn't have a way to know to keep triple quotes.

[randombyte-developer]

I suggest rendering triple quotes if the string contains at least one quote. This behavior could be always enabled or by some sort of render option, so for the whole file. The original formatting of the specific node doesn't need to be known.

SpongePowered/Configurate#96

@havocp Should I do an attempt for a PR? I would implement it somewhere here.