New formatter for XML: Jackson

[eirnym]

Jackson has ability to read and write XML and it has many formatting options.

Could you please, add the xml formatting using Jackson

[blacelle]

Related work has been done for YAML and JSON (through Jackson). The effort for XML would be smaller (as common jackson-tooling is setup. See #1508

@eirnym Would you consider a PR?

[eirnym]

Thank you @blacelle, will do