Allow Admonition variant types to be case insensitive

[michael-nok]

When specifying an Admonition note, the variant type must be specified in lowercase.

This causes some confusion given the output of the variant may have an uppercase starting letter.

• !!! note renders as Note:
• !!! Note renders as OTHER: Note.

File: CoreNodeRenderer.java - Line 405

Please consider changing:

final String type = node.getInfo().toString();

to:

final String type = node.getInfo().toString().toLower();

switch statement:

        switch (type) {
            case "note":
            case "tip":
            case "fastpath":
            case "restriction":
            case "important":
            case "remember":
            case "attention":
            case "caution":
            case "notice":
            case "danger":
            case "warning":
            case "trouble":
                atts.add("type", type);
                break;
            default:
                atts.add("type", "other").add("othertype", type);
                break;
        }