* Fixed typo
* Added proper exceptions for publishers
* Updated publishers logics: using messengers to allow publications without events
* Added new exception 'InvalidSettings'
* Updated notifiers and publishers: retrieve credentials and destination from config, use only message/event in constructors, lesser refactoring
* Updated publishers' tests
* Updated notifiers and publishers config for Telegram service, updated settings.toml file
* Updated 'post()' method and removed useless config checks for Telegram bot
* Added jinja2 template management for message formatting methods
* Manage message validation in publishers' run() method
* Better config management for notifiers and publishers
* Lesser update to logging and error-raising management (#23)
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