Update docstring and type hint for lambda_handler

[nikhilym]

Description

Update the type hint for skill_builder's lambda_handler , to reflect the (de) serialization component. Also add docstring information to mention how the lambda_handler is processing the input from AWS Lambda.

Motivation and Context

Fixes #93 . Since sb.lambda_handler is specific to AWS Lambda, the underlying function should only accept parameter types specific to Lambda processing. So changing the type hinting to reflect that. Also mentioning more information on how this is processed in the skill code.

Testing

Generated sphinx docs locally to check the docstrings. Checked the automated documentation in IDE's to reflect the type hints. Since the lambda_handler function is a wrapper function and the actual type hints are on the wrapper, the IDE doesn't show any hints for the lambda_handler function itself. mypy tests on ask-sdk-core also passes through travis.

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[pbheemag]

nit: serialized to* (in the function description)

[nikhilym]

@pbheemag thanks for the comment.

nit: serialized to* (in the function description)

However, I don't think I need to add a to here because I mention that the output is the serialized model class.

[nikhilym]

Travis build is fine. Looks like github integration with travis is facing problems. So going ahead with merging this change.