Add PETL-based formats

[roll]

Overview

As we already have PETL as a dependency we can add support for Whoosh, Avro etc formats relatively simple.

v5 file structure

formats
  avro  # just proxy PETL parser
  whoosh  # just proxy PETL parser
  ...

https://petl.readthedocs.io/en/stable/io.html#module-petl.io.xls