Add functionality to send event to multiple addresses at once

[JustArchi]

Closes #8

[iamtraction]

I'll test & review this before I merge. Is it a breaking change? Will it affect users who are already using this?

[JustArchi]

No, this is not a breaking change, existing setups will work as before. The main difference is how previously WEBHOOK_URL: "addr1.com addr2.com" didn't work at all, and now works as expected, by sending a webhook update to addr1.com and addr2.com.

Of course you're more than welcome to test this change, but unless somebody is using a webhook with space in the URL, this should not regress on any setup. And even if somebody has spaces in his URL, he should escape them with %20 anyway as required by RFC - and then it'll work as before.

[iamtraction]

Thanks for the contribution, would you also like to implement this in appveyor-discord-webhook, gitlab-ci-discord-webhook, and github-actions-discord-webhook?

[JustArchi]

Sure thing, I'll do last 2, I'm not entirely sure how to do it in powershell as my knowledge is more limited there. Feel free to cover the first one if you'd like to, as the concept is similar 👍

[iamtraction]

Cool, thanks. Also, I won't be taking up the task as I want to open it for Hacktoberfest for new contributors. So, if anyone else wants to take it, feel free to do so: DiscordHooks/appveyor-discord-webhook#14