lib/standard/string: NativeString methods now return String instead of FlatString.

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
lib/ropes: Introduce ropes everywhere module, which enables use of Ropes for a lot of operations instead of FlatTexts.

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
nitg_ropes: Added new engine, same as nitg, but using Ropes for a majority of operations.

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