internally handle rate-limit

[Xiphe]

fix https://github.com/cemalgnlts/Mailjs/issues/15

[Xiphe]

pre-published as @xiphe/[email protected]

[cemalgnlts]

This is a great feature. But we won't need the second commit (add rate-limit even), SSE (events) works differently and we will not have a problem with rate-limit.

[Xiphe]

Hi @cemalgnlts, thanks for the feedback, glad you like it!

Ok, that's cool with me. I added that feature to debug why the lib doesn't work in CI (seems as if I'm not the only one trying to use that service from github actions and therefore run in a LOT of rate-limiting).

Will remove that commit and the custom backend support into a separate pr later.