Move type definitions to separate header file

Include header file 'aimn91.h'
Update file info and comments

also remove spaces at the end of some lines.
Change names to shorten lines

Change 'FORWARD' to 'F' and 'BACKWARD' to 'B'.
Change 'vertex_in_graph' to 'v_in_g' and 'parent_in_tree' to 'p_in_t'.