Ahaggar: add the output_swap_meta() declaration

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Ahaggar: define the output_swap_meta() function

This function is used to swap the meta data of two output_buffer
structures.

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Ahaggar: add the str-utils.h file that declare string utilities

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Ahaggar: define string and substring utilities functions

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>