corrected issue with delete at end of a line

was incorrectly setting the modified line type as inserted when the
next line was blank - added check if characters were added
corrected issue with backspace or deleted at newly inserted line

was incorrectly reporting a line as being deleted, but a line hadn't yet
been reported as being inserted yet - added check if line was newly
inserted, to reset the new line flag and prevented an empty lines
changed signal
changed modified line type variable to a boolean

the line type enumeration only had two values, so it was removed and the
modified line type variable was changed to a boolean and renamed to make
the code more readable
corrected the reporting of deleted lines

if there was a changed line along with deleted lines in the line
changed signal, the wrong number of lines were reported as deleted