added generate_doc signal & handler for it generate_doc_handler
Merge branch 'develop' of https://github.com/allegro/ralph_assets into post-hook
post transition as signal instead of fn calling signal
Merge branch 'feature/hostname-transition' of https://github.com/quamilek/ralph_assets into post-hook

Conflicts:
	src/ralph_assets/views/transition.py
added tests; dirty version
added test 'post_transition fails' & code cleanups
Merge branch 'develop' into post-hook

Conflicts:
	src/ralph_assets/tests/functional/tests_transitions.py
another cleanups
rm max_length in bulk's hostname
added docstring and part of documentation
added signal receiver example
Merge pull request #358 from xliiv/post-hook

post-transition-signal