Merge branch 'release/0.2'
some updates bugfixing
fixed stacktrace pruning but lost python3 compatibility
removed current stacktrace pruning because there is no Python3 compatible way of doing it
Merge branch 'master' into develop

Conflicts:
	sacred/commands.py
extracted _warn_about_suspicious_changes method
made _emit_info_updated auto repeat every 30sec and added a heartbeat field to db entry
added output capturing and also added it to the db entry
fixed tests
refactored and fixed and added DebugObserver
added log level flag. fixes #4