Tests: Pretty-printed token stream

[RunDevelopment]

This adds support for pretty-printed simplified token streams via the --pretty modifier.
E.g. npm test -- --pretty or npm test -- --language=xxxx --pretty

Only the current token stream of failed tests will be pretty-printed. This can then be copypasted into .test-files.
Because most consoles convert tabs into 8 spaces, I used 4 spaces for indentation.

This should make writing tests a lot more comfortable.

Example

Now:

[["tag",[["tag",[["punctuation","<"],"div"]],["attr-name",["class"]],["attr-value",[["punctuation","="],["punctuation","\""],"test",["punctuation","\""]]],["attr-name",["foo"]],["attr-name",["bar"]],["attr-value",[["punctuation","="],"baz"]],["punctuation",">"]]]]

Pretty:

[
    ["tag", [
        ["tag", [
            ["punctuation", "<"],
            "div"
        ]],
        ["attr-name", [
            "class"
        ]],
        ["attr-value", [
            ["punctuation", "="],
            ["punctuation", "\""],
            "test",
            ["punctuation", "\""]
        ]],
        ["attr-name", [
            "foo"
        ]],
        ["attr-name", [
            "bar"
        ]],
        ["attr-value", [
            ["punctuation", "="],
            "baz"
        ]],
        ["punctuation", ">"]
    ]]
]

[mAAdhaTTah]

minor nit but gtg