Support strings for keys

[brettlangdon]

Right now we are limited in how we can name settings, basically [_a-zA-Z]+ is all we allow.

I have been thinking about allowing strings as identifiers. To allow for more complex key names.

"some-key@name" = "it's value";

Will probably keep references strict to just unquoted identifiers for now.

[brettlangdon]

Just making note, allowing quoted keys in references would end up looking like: "some-key@name"."another-key", I haven't thought of anything better.

[brettlangdon]

Well... looking at it again, unless we do "some-key@name.another-key" which is much better looking, but think it could be very easily confused.

[jeevatkm]

Allowing . in the keys is practical and helpful in real usage. No impact on references. However not sure of @, -, etc.

For example: Let's say we have only one identifier in nested namespace. Allowing . will transform following-

markdown {
  cache = true
}

into

markdown.cache = true