Pos tag threshold

created a class for checking the precision, recall and f1-scores by predicting errors in sentences.

requested review from @stjemahz, @stcorent, @stheraib, @stnoschab, and @isttipach

assigned to @isttipach, @stjemahz, @stcorent, @stheraib, and @stnoschab

mentioned in commit 9cd37f64

merged