Sprintf formatter plugin for Embulk

Formats Sprintf(Java String#format) files for other file output plugins.

• Plugin type: formatter

• format: format (string, required)
• column_keys: column_keys (array, required)
• null_string: null_string (string, default: '')

out:
  type: any output input plugin type
  formatter:
    type: sprintf
    null_string: null
    format: "    - { id: %s, url: '%s' }\n"
    column_keys:
      - id
      - url

$ ./gradlew gem  # -t to watch change of files and rebuild continuously