Add pluggable output formats and README docs (#format)

[Sergpoipoip]

Add pluggable output formats (via #format + addon converters) and update README

This PR introduces a pluggable output-format pipeline in ramose.py and documents it in README.md. It lets API authors return responses beyond CSV/JSON (e.g., XML, Turtle, N-Triples) by mapping format → converter function in the top-level #format of the .hf file, with converter functions implemented in the #addon module.