[lib] Add Dart library

[nebkat]

Have now published my Dart BJData encoder/decoder! 🚀

---

One of its unique features that it offers is encoding to block-notation:

Input:

{
    "foo": 1,
    "bar": 2
}

Tool:

dart pub run bjdata block example.json

Or function:

bjdataBlockNotation(input);

Output:

[{]
    [U][3][foo][U][1]
    [U][3][bar][U][2]
[}]

Very useful for debugging without having to get the hex editor out 🤓