* Implemented should_sign_header callback

* Added SigV4A to SigningAlgorithm

* Added SigV4A test

* Added debugging info to README

* Fixed memory leak from argument vectors

* Fixed memory leak of stream read buffers

* Added support for callables as option values

* Added should_sign_header support and test

* Fixed ELG type bug exposed by aws-crt-ffi change

* Updated to aws-crt-ffi v0.2.0