lib/standard/ropes: Removed ropes.nit from standard library

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
lib/standard/ropes: Ropes rewriting

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
lib/standard/ropes: Introducing Leaf, a buffered FlatString with a fixed size

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
benchmarks: Benches adapted to new Ropes

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>