Cleaning up DocumentWriter()

we do not use this class anymore, instead we now use the dedicated class
"TransportationListDocumentWriter()" (which, yes, is a mouthful).

DocumentWriter was used from the class DistanceMatrix, which was okay in
'ye 'olde 'days, now it seems like a mistake and the control is passed
on to Form().
Merge branch 'master' of https://github.com/vvim/routetool