Added `middleware` and `config` examples; reorganized

Squashed the following commits:
Demonstrate how to access session data in view.

Adding example using `config` module

Renamed examples to indicate order of progression

Incorporating 01_config's changes into 02_sessions

Actually use `config.server.port`

Adding `middleware` example.

Better way of using middleware for `sessions` example.

Remove `runtime.json` file
Merge pull request #134 from airbnb/examples

Added `middleware` and `config` examples; reorganized