Fixed documentation for PackageConfig.env attribute

Previously the documentation incorrectly stated that env attribute's value is used only when packing in Docker container, which is not correct.

Refactored DockerConfig to general PackageConfig and added tests

BREAKING CHANGE

DockerConfig class was replaced by general PackageConfig class to provide single unified interface for configuring packaging process.

Enhancements

• Added unit tests
• Added coverage
• Improved documentation with deep links

Packaging and documentation improvements

• Moved cdk_chalice module outside of package, to generate consistent documentation with usage
• Refactored version and metadata to be managed in a single source-location
• Minor documentation improvements

Additional packaging features and coverage

Support custom Docker image for packaging the Chalice app (contributed by @cohen-elad)
Support for packaging all Chalice-generated Lambda functions (contributed by @alexgelman)
Documentation improvements

Packaging in container + API documentation

• Added supported for packaging the Chalice application in AWS Lambda-like environment.
• Published API documentation to Read the Docs

Initial version

Initial version. Features include:

• Support for Chalice API handler Lambda functions only
• Specifying an existing IAM role for Chalice API handler Lambda function or let cdk-chalice create one
• Additional environment variables can be passed to Chalice API handler Lambda function