Fix sam local support for missing headers (awslabs#38) (awslabs#332)

* Added unit tests for TryFrom<HeaderMap> for Context

Fix license field for lambda_runtime (awslabs#302)

The license field for lambda_runtime was not using the correct
identifier preventing publishing to crates.io.

Preparing for 0.2 release (awslabs#75)

* Added errors and derive crate to workspace and exported derive crate from errors crate

Release 0.1.0 of Lambda runtime client

Release 0.1.0 of lambda-runtime crate