Gather the plain flavour's code in markdown/plain/

src/index.ts

@@ -3,6 +3,6 @@ export type { AdfAttributes, AdfDocument, AdfMark, AdfNode } from './adf/documen
 export type { ConvertError, ConvertErrorCode, ConvertErrorPath, ParseError, Result, SourcePosition } from './result.ts'
 export type { JsonValue } from './json-value.ts'
 export { adfToMarkdown } from './markdown/emit/adf-to-markdown.ts'
-export { adfToPlainMarkdown } from './markdown/emit/plain-reduction.ts'
+export { adfToPlainMarkdown } from './markdown/plain/adf-to-plain-markdown.ts'
 export { isAdfDocument } from './adf/document.ts'
 export { markdownToAdf, plainMarkdownToAdf } from './markdown/parse/markdown-to-adf.ts'