Render valid JSON with an option

[mohsen1]

When valid attribute is present, render a valid JSON that can be copied

• remove constructor names from DOM tree and put them in :after elements so it doesn't copy
• remove functions and values that are not valid in JSON. undefined, NaN, Infinity, (will be null)
• add {, }, [, ], , where it's necessary to make JSON valid
• write test that test produced HTML has valid JSON in it's innerText

[mohsen1]

Moved from mohsen1/json-formatter#17