JSON-compatible error outputs

[JohnnyMorganz]

(Converting to an issue so I do not keep forgetting, originally requested by @telemachus in #93 (comment))

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We now have a --output-format=json flag, but this currently outputs diffs in json when using --check, not errors.

We could update the env-logger builder to output json for general errors in https://github.com/JohnnyMorganz/StyLua/blob/master/src/cli/main.rs#L327-L353, but we would also want to special case error handling for parse errors (so that we can return data about the location) at https://github.com/JohnnyMorganz/StyLua/blob/master/src/cli/main.rs#L79-L80 and https://github.com/JohnnyMorganz/StyLua/blob/master/src/cli/main.rs#L118-L119

I was thinking of an error structure something like

{
    "type": "error", // or "warn"/"info"/"debug" etc. and "parse_error"
    "message": "XYZ"
}

and if type == "parse_error" we also have a filename and location field like

{
    "type": "parse_error",
    "message": "XYZ",
    "filename": "src/test.lua",
    "location": {
        "start": 0, // byte offset from start of file
        "start_line": 0,
        "start_column": 0,
        "end": 0, // byte offsets from start of file
        "end_line": 0,
        "end_column": 0,
    }
}

Originally posted by @JohnnyMorganz in #93 (reply in thread)