[proposal] Rest API with multiple lambda functions

## Overview ##

The current state of the framework deploy the entire project into a single lambda function instance. But for larger projects this can be a problem for several reasons:
- Monitor individual lambda routes integration (number of invocations, errors, etc).
- Controlling individually the lambda functions (permissions, throttling, etc).
- For optimize the lambda function deployment package (.zip).
- If there is an error with one function, the other ones will not be affected.

## Register Handler class ##

The routes will be registered from each handler that will be implemented separately. Below is an example of the hello handler:

Example of usage:
app.py
```python
from chalice import Chalice

app = Chalice(app_name="helloworld")

app.registrate_route(
name='hello_world',
path='/helloworld',
handler_class=HelloHandler,
)
```
hello_world.py
```python
from chalice import LambdaHandler

class HelloWorldHandler(LambdaHandler):

def get(self):
return {"hello": "world"}
```

To make packaging possible, the project directory must be structured in a specific way.
as follows:
```

├── helloworld
│ ├── functionlib # function specific modules
│ │ ├── __init__.py
│ │ └── utils.py
│ ├── __init__.py
│ └── helloworld.py
├── chalicelib # project shared modules
│ ├── __init__.py
│ └── generics.py
├── app.py
├── requirements.txt
└── etc ...
```

Start with the app.py registration example and the proposed hello_world.py handler, then compare them with Chalice's current deployment and packaging behavior. Review the proposed project layout, including functionlib, chalicelib, and requirements.txt. Done would mean independently deployable Lambda functions with routes registered through separate handlers.

Written by the indexing model from the issue text.