rename files so that each module & its tests are grouped

Signed-off-by: Wilfried Chauveau <ithinuel@gmail.com>
add mm_chunk_next_get & mm_chunk_prev_get, change mm_to_csize from uint32_t to uint16_t

Signed-off-by: Wilfried Chauveau <ithinuel@gmail.com>
split return the created chunk or null.

Signed-off-by: Wilfried Chauveau <ithinuel@gmail.com>
restart memmgr implementation

Signed-off-by: Wilfried Chauveau <ithinuel@gmail.com>