Fix bug of impulses for damage
Replace distance-joints with weld-joints
Rename Entity.WorldCenter() Entity.worldCenter
Assign empty dict to userData if it's None
Change APIs around Entity.render and appearances
Fix a possible crash for index and a object leak
Set bullet flags on fireballs
Fix some bugs
Make poppies weak
Add fixture.userData['render']() as a callback
Add body.userData['render'] callback too
Change classic classes to new-style classes
Add 'update' callback for bodies and fixtures

Rewrite dragon's flying with it. It stops when not only their trunks but
also their heads died.
Add fixture destroying to Entity.update()

update() of Dragon and Poppy is removed for it. Player's one does not
call the super now. I'll fix it soon.
Rename Rein.nodes to Rein.objects

The name matches Rein.append_object and Rein.remove_object.
Improve player very much

- Player stability is increased.
- Player stand only when he touch a ground.
- Player can die.
Follow pylint

- Rename many Entity's methods as snake_case.
- Modify many small things.
Write some docstrings

- Entity class has enough docstrings now.
- Includes fixing of a hidden bug made at previous commit.
Merge branch 'master' of github.com:canagh/rein

I have no idea why this conflict happend, because I'm a begginer yet.

Conflicts:
	rein/entity/__init__.py