Prototype

Here is the first steps of the prototype, it's a rough draft of my idea.

Commands that you should try and should work from the console:

```ruby
# enter the console
cd spec/dummy && rails c

# You might need to run a migration inside the dummy app before entering rails console
rake db:migrate

# create a post to play with if you don't already have one
p = Post.create(user: User.first)

# get to the activity
p.activity

# this part is done automatically, but this is how an activity is created
a = ChooChoo::Activity.create(parent_node: p) 

# get all the activities with the latest one first
ChooChoo::Activity.order(updated_at: :desc)

# get the top node of the last activity
ChooChoo::Activity.last.parent_node

# get the model the latest event happened to
# will currently always be the same as parent_node
ChooChoo::Activity.last.last_updated_node
```

**UPDATE**

There is now support for viewing it in the browser.

To create some dummy posts and comments run:

    rake app:db:seed

Then fire up the dummy app!