Introduce rake and Centroid

This refactors the repository to use `rake` to drive all automation. Centroid and `config.json` keep the Simpler specific information out of the Rakefile.

The rake tasks are shown below.
```
$ rake -T
rake build:debug    # Build for debugging
rake build:release  # Build for release
rake bump:major     # Bump major version
rake bump:minor     # Bump minor version
rake bump:patch     # Bump patch version
rake clean:all      # Clean all output
rake clean:release  # Clean release output
rake clean:test     # Clean test output
rake default        # Run tests
rake install        # Install NuGet dependencies
rake release        # Pack and push NuGet package
rake release:pack   # Pack NuGet package
rake release:push   # Push NuGet package
rake test           # Run tests
```

Tasks
- [ ] Document details of how everything works in a CONTRIBUTING.md file.
- [ ] `bump` tasks only work on Windows.

This will close #18.