Improve rendering of dataset.meta properties (close #280)

[tcompa]

Checklist before merging

• I added an appropriate entry to CHANGELOG.md

[tcompa]

As of 741048b, setting dataset.meta to

{
"null": null,
"string": "string",
"boolean": true,
"number": 3,
"array[string], length 1": ["item"],
"array[string], length 2": ["item1", "item2"],
"object[string,string], length 1": {"key": "value"},
"object[string,string], length 2": {"key1": "value1", "key2": "value2"}
}

leads to