Django-sitemessage

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* Django 1.10 compatibility improved.

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+ Implemented VKontakte messenger.
+ Implemented Facebook messenger.

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* Template compilation errors are now considered dispatch errors and properly logged.

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* Django 1.9 compatibility improvements.

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+ Implemented Telegram messenger.
+ Added `allow_user_subscription` attr to base message and messenger classes.
+ Added schedule_tweet() shortcut.
+ Added schedule_telegram_message() shortcut.
+ Added Messenger.before_after_send_handling() context manager.
* Fixed `get_user_preferences_for_ui()` producing buggy result.

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+ Adapted for Django 1.8.
* Russian locale is updated.