HtmlEscapeMode constructor
Create a custom escaping mode.
All modes escape &.
The mode can further be set to escape < and > (escapeLtGt),
" (escapeQuot), ' (escapeApos), and/or / (escapeSlash).
Implementation
const HtmlEscapeMode(
    {String name: "custom",
    this.escapeLtGt: false,
    this.escapeQuot: false,
    this.escapeApos: false,
    this.escapeSlash: false})
    : _name = name;