Enforce lowercase GitHub owner name

• For GitHub Docker registry, converts owner name to lowercase per these restrictions
• Bump @actions/http-client from 1.0.7 to 1.0.8

Add support for custom build directory

• Add directory input parameter for docker build commands outside project root

GitHub Docker Registry support

• Adds GitHub Docker Registry support
• Add imageName and tag outputs
• Begin piping logs for docker build and docker push to console

Docker build args support

• Adds support for Docker build args
• Increases buffer size for child_process.execSync() to support large Docker builds

v1.0

• Support for Docker Hub, GCR and ECR
• Configurable Dockerfile name and location