The memory buffer already supported appending and prepending data, but
not inserting data anywhere in the buffer. That's exactly what the new
function does. The free space is still maintained at either the start or
the end of the buffer.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.