Add gif personalization support on events.

[riolcrt]

Add the option to customize the image shown in twitch live by including a tag in the text of the issue with the url of the gif. Applicable also for any type of event.

For exampl by including something like:

This is my issue text
[gif-url = https: //media.giphy.com/media/jUwpNzg9IcyrK/giphy.gif]

[SantiMA10]

@all-contributors please add @riolcrt for ideas

[allcontributors]

@SantiMA10

I've put up a pull request to add @riolcrt! 🎉