Code meant for the move_to_next_word functions which set the cursor to
the last character in the file if it was reached was copied into the
move_to_previous_word functions which lead them not moving when
the function was called from the end of the file.
Implemented move_to_beginning_of_next(), move_to_end_of_next(),
move_to_beginning_of_previous() and move_to_end_of_previous() functions
for more correct word jumping than the move_to_xxx_span() methods that
were previously used.
