Maintain comments, formatting when dumping YAML

[jewzaam]

Not everybody using the hiera data will be looking at monarch files. While it's good to have comments in the changeset we loose the ability to comment the hiera yaml. This can help folks understand why something was set etc.

[alechenninger]

This would be great, unfortunately it requires a YAML parser which parses extra metadata about the YAML document like whitespace and comments, and maintains that when dumping.

I considered using a YAML merge tool like https://github.com/geofffranks/spruce or something. This may do the trick. This sorts elements alphabetically too.

[alechenninger]

I looked into this some more, there is not a good option for Java. There is a good option for Python though, so I may consider porting the library to Python, which has better support for CLI apps anyway: http://yaml.readthedocs.org/en/latest/overview.html

[alechenninger]

Note the above yaml library's preservation of formatting is not perfect:

This preservation is normally not broken unless you severely alter the structure of a component (delete a key in a dict, remove list entries). Reassigning values or replacing list items, etc., is fine.

[alechenninger]

#42 is implemented which helps. I think I can make this work for comments without too much effort, but not formatting. Comments are probably more important to maintain than formatting, though.