Ignore empty lines inside the BIO files

This MR introduces support for BIO files with empty lines

Louis B-PER
par I-PER

la I-PER

There was an issue because it tried to split on in that case, we should simply skip such lines.

added P1 label

requested review from @starride

assigned to @yschneider

requested review from @mboillet and removed review request for @starride

approved this merge request

merged