Skipping lines

[Arnau478]

Add an option to skip all lines that are exactly the same as both the previous and the next one.

Example

dead beef dead beef dead beef dead beef
dead beef dead beef dead beef dead beef
dead beef dead beef dead beef dead beef
dead beef dead beef dead beef dead beef
dead beef dead beef dead beef dead beef

would turn into something like

dead beef dead beef dead beef dead beef
... 3 lines skipped ...
dead beef dead beef dead beef dead beef