* Add Mastodon publisher.
This commit enables publishing on Mastodon and tries to define the
minimal requirements for adding a new platform to Mobilizon Reshare.
* publishers: exceptions: Add HTTPError.
* platforms: mastodon: Make toot length customizable.
* added basic recap feature (no error handling)
* introduced abstractpublication
* extracted base reports
* added error report to recap
* added test
* added docs
* implemented publisher and formatter
* fixed API for recap
* removed redundant config validation
* added config sample
* added mobilizon link to templates
* added link format to telegram
* added mobilizon link to recap
* fixed config and emoji
* decoupled notifiers from event
* stub
* publishers working
* fixed format CLI
* fixed unit tests
* renamed abstractnotifier
* added another excluded character
Giacomo Leidi
Simone Robutti