Prepare 2.0 release and changelog

[scarlehoff]

The main features of this release (and the reason it qualifies for a major version change) is the addition of the facebook backend (PRs #11 and ??). A lot of documentation has been added to that respect (see: ). Basically it should be possible to do the same now with Facebook Msgs and a Telegram bot.

The code has been refactored (#6, #8, #10), some docs updated (#9) and a test-backend plus CI added (#7).

In term of functionalities (of what can one do with this code), not much has changed since 1.3, arguments are now passed to the scripts (#14) and some clean up here and there.

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Before doing the release docs for facebook #12 need to be added.
Allowing for multiple attachment (#13) would be nice but not really required.