Provide abstract class over certain implementation details

[formrre]

We should provide an abstract interface, which would allow the user to pick'n'mix implementation details, pick'n'mix should simplify benchmarking these different variants

List of choices to provide:

• eager or lazy deletion of arbitrary items
• eager or lazy filling
• unary node filling by replacement or normal filling
• even recursion-level filling instead of even-rank filling

Extra:

• allow whole implementational variations for benchmarking the code, compare Chazelle (1997), Kaplan&Zwick (2009) and the current implementation based on Kaplan,Tarjan and Zwick (2013)