Add a RTF editor to the Compiler IDE

Inno Setup requires .RTF for rich text shown by Setup, because Windows has no built-in support for showing other rich text formats like Markdown. At the same time, Microsoft removed WordPad, making it harder to create .RTF files. One option is LibreOffice, but this requires installing extra tools.

Add a simple WYSIWYG RTF editor to the Compiler IDE to fix this. It does not need to be feature-rich, but should cover the basics needed for a info and license files.