Support for CTA text

[gijo-varghese]

FB's STM button now allows setting custom CTA text.

Is this possible?

Details: https://developers.facebook.com/docs/messenger-platform/discovery/send-to-messenger-plugin/#approved-CTA

[lemieux]

That's most likely very possible, but I don't have much time to work on this library currently. PRs are welcome though and I take time to cut new releases when PR are merged. :)

[gijo-varghese]

Ok. I'll do that. What about this one? #14