Automatically generate code-blocks for Github gist links in chat #60

Description
Allow inlining of code blocks from GitHub links that have highlighted lines.

Example

Dioxin says:
Check this out:
https://gist.github.com/discorddioxin/27a33cf1376847f4ada29d61390c5198#file-main-java-L13-L16

Bot says:

        box.getItems().add(new Student("First", 111, 3));
        box.getItems().add(new Student("Second", 222, 4));
        box.getSelectionModel().select(0);

→ https://canary.discord.com/channels/648956210850299986/752535909228085348/867505817506414593