Make gem useable by unitsml gem

[ronaldtse]

We are blocked by these issues:

• feat: added root_mappings option lutaml/lutaml-model#222
• (URGENT) YAML boolean type values not working when set to false lutaml/lutaml-model#225
• When imported data contains a blank (extant but nil values) item, the value serialized is a {} which is not allowed in YAML lutaml/lutaml-model#226

Once these are resolved, we need to implement the necessary changes and this gem is good to go.

We also need an API that allows the unitsml gem to use it.

Originally posted by @ronaldtse in #2 (comment)