Insert, align, or delete end-of-line backslashes on the lines in the region.
With no argument, inserts backslashes and aligns existing backslashes.
With an argument, deletes the backslashes.
This function does not modify the last line of the region if the region ends
right at the start of the following line; it does not modify blank lines
at the start of the region. So you can put the region around an entire
shell command and conveniently use this command.