example_client, lot of refactorings and changes

Makefile modified to allow building of example_client.
Added plan.txt to track TODO lists and architecture thoughts.
Protocol structures and some constants moved from bm_parser.h to
bm_parser.c.
Payload read/estimate/write/free functions made external with prototypes
in bm_parser.h.
Improved BM_DEBUG_LOG macro (dropped compatibility with C standard for
debug build).
Generalized item list handling.
Implemented addr payload support.
Implemented inv_vect payload support.
Many refactorings and improvements.
example_client incomplete implementation for real-world functional
testing.