Github Workflows

Adds automated testing and builds to this project via Github Workflows.

Workflow descriptions

Testing.yml

Runs cargo check to ensure that the binaries compile
Runs cargo fmt --all --check to ensure that the project has been formatted
Runs cargo clippy to ensure that the project has been linted (ignores warnings)
Runs cargo/cross test --release --target ${{ matrix.target }} --verbose to ensure that all tests pass for various targets:
- x86_64-unknown-linux-gnu
- x86_64-unknown-linux-musl
- x86_64-apple-darwin
- x86_64-pc-windows-msvc
Release.yml
- Builds release binaries for various targets:
- x86_64-unknown-linux-gnu
- x86_64-apple-darwin
- x86_64-pc-windows-msvc
- Builds berkshire_hog_lambda release binary for x86_64-unknown-linux-musl
- Builds Docker images for each hog
- Publishes release binaries for each target
- Publishes berkshire_hog_lambda release binary for x86_64-unknown-linux-musl
- Publishes scripts directory
- Pushes Docker images to each respective Docker hub repository

Added files for builds:

Removed unused files:

.travis.yml
build_docker.sh (moved logic to Makefile)
build_ghrelease.sh (moved logic to release.yml)
build_lambda.sh (moved logic to release.yml; will update manual lambda build instructions in next commit)
Dockerfile (split into Dockerfile.build and Dockerfile.hog, for build time efficiency)
entrypoint.sh (entrypoint is defined in Dockerfile.hog)