* add support for ECDSA keys
* Add support for HTTP signature
* use bytes.Buffer instead of strings.Builder
* Add unit tests, compliance with HTTP signature draft version 12
* Support (expires) parameter
* Validate list of signed headers does not have duplicate values
* move method to ProcessUtils
* Add http-signature security scheme
* add http_signature_test to security scheme
* remove http signature from petapi
* Add separate OAS file with support for HTTP signature
* Include HTTP signature in README file
* Add generated files for HTTP signature
* Add helper function to return public key, and add more unit tests for signature validation
* some people save their private key with file extensions other than .pem, so I am relaxing the validation of the private key suffix
* Add debug flag for go-experimental generator
* Check for errors before dumping the response in Go generator
* samples/openapi3: update samples for Go generators
