Rename `folio-mafsa-common-prefix' from `folio-mafsa-previous-word' as
this describes its purpose better.
Add doc-strings.
Rename `folio-intersect-mafsa' from `folio-mafsa-intersect'.
Add `folio-map-mafsa' for traversing an FSA.
Rename `folio-lookup-dictionary' from `folio-dictionary-lookup'.
Add `folio-map-dictionary'.
Add doc-strings.
Add `folio-mafsa-state-id'.