Break out of IAM policy generation to separate module

While looking at this project's description I noticed the ability to generate IAM policies was present. Doing code analysis of python based Lambdas and looking for boto calls to help generate IAM policies easily is something I've been considering for a long time and was pleased that the groundwork was essentially laid out, specifically:

https://github.com/aws/chalice/blob/master/chalice/analyzer.py

The analysis of the AST for boto calls I think would be more beneficial as a separate module. That way processes could be built around python Lambdas to generate IAM policies automatically. As it is now such tools would have to pull in potentially unrelated code for API Gateway. Curious on your thoughts regarding this.

Start with chalice/analyzer.py and trace how IAM policy generation is coupled to API Gateway analysis. Determine the intended module boundary and how a standalone consumer would use the IAM analysis; done means the separation is clearly defined and the existing behavior remains covered.

Written by the indexing model from the issue text.