feat: separate field + node to access strings content

[ahlinc]

This PR is a proposal, but I'm not sure that it's worth to merge it.

Resolves #101

[verhovsky]

I appreciate it but it's more complicated than just removing the quotes, especially for ANSI-C quoted strings. You have to also remove stuff inside the string, like escaped quotes (replacing a backslash and a quote with just the quote) and newlines (which are removed). You can see how I ended up doing it here

https://github.com/NickCarneiro/curlconverter/blob/265a9372c6f9d361c820daba33e3b4b3906685bb/util.js#L557-L643

I especially spent a lot of time getting the ANSI-C quoted string parsing correct for this PR (which is ultimately probably not going anywhere...) yargs/yargs-parser#366

[ahlinc]

@verhovsky Got it, thanks for the link to the code. Such processing isn't possible in tree-sitter because tree-sitter doesn't store any resulting values in its nodes. It's AST nodes are just references to the concrete places in a source code. In sight of this the #101 issue I suppose can be closed.
P.S: It's possible to write some sort of string parsing on tree-sitter but only with possibility to skip some input parts and gather resulting value by concatenating in a buffer values from the nodes.