Small incremental release

A small incremental release with the following changes:

• Added equals() and hashCode() to WrappingMap to simplify unit tests
• Added convenience methods of(), combine() and withReplaced() to YAMLMapping to create instances
• Added method YAMLUtil.allFromPath() that parses all YAML documents from the file referenced by the provided path
• Implement support for null values
• Set up build pipelines using circleci