topic_report: fiddle parameters and roxygen docs
topic_report: fiddle parameters and roxygen docs

No longer requires you to pass in dtl and dtw; instead, calculates them
from the normal dt frame and metadata.

agoldst/dfrtopics,agoldst/dfrtopics,agoldst/dfrtopics,agoldst/dfrtopics,agoldst/dfrtopics,joncgoodwin/dfrtopics,joncgoodwin/dfrtopics,joncgoodwin/dfrtopics