Add idHandler.transformtoSourceIds
Add idHandler.transformtoSourceIds

Takes tokens and an docIdentifier, returns an object with mappings to
the source document and an array with unmapped tokens.

alpheios-project/arethusa,fbaumgardt/arethusa,latin-language-toolkit/arethusa,PonteIneptique/arethusa,fbaumgardt/arethusa,PonteIneptique/arethusa,latin-language-toolkit/arethusa,fbaumgardt/arethusa,alpheios-project/arethusa,Masoumeh/arethusa,alpheios-project/arethusa,Masoumeh/arethusa