Adding 2 functions: moving_sums and moving_means

[tshev]

moving_sums takes 3 input iterators, output iterator and returns an output iterator. moving_means takes 3 iterators and returns a vector by value.

How to use:

• origin::moving_means(f, f + win_len, l);
• origin::moving_sums(f, f + win_len, l, output_it, acum);

Some examples