Port GitHub code display embed from Python
Move the feature that displays the lines of code from GitHub when a link with line numbers is sent from Python to Sir Lancebot
Approved by @Xithrius here: https://discord.com/channels/267624335836053506/635950537262759947/997558518968221696
I approve here as well.
For reference, this is the location of said feature.
@shenanigansd has stated in #dev-contrib that they're not wishing to implement this themselves, so I'd like to claim this. Can I please be assigned?
NB: This is now waiting on python-discord/bot-core#141, as lancebot is missing certain util functions.