New 2 spaces and no tabs formating for list.hpp
New 2 spaces and no tabs formating for arithmetic.hpp
New 2 spaces and no tabs formatting to common.hpp
New 2 spaces and no tabs formatting for sequence.hpp
Delete first algorithm implemented.

Implementation of delete first algorithm over sequences.
Tests added for sequences and for lists.
Delete firsts implementation

Delete firsts algorithm implemented.
Tests added over lists and over sequences.
Formatting some comments