libmemdisc: introduce pointer to heap discovery

If we already know the pointer to a memory object on the heap, it
would be really cool to use the pointer value for discovery. This
pointer may be within static memory or another heap object. When
the pointer and its value are valid, we want libmemdisc to report
the pointer value through the FIFO.

This is especially useful if we could discover a parent object but
can't find values within the child object. Getting the child object
from the pointer would enable us to compare the memory object dumps
of different states.

Example: Warzone 2100: functionality pointer in class Structure

Discovery string prefix:
"p;<malloc_size>;<code_addr>;<stack_offs>;<ptr_offs>;;"

For a pointer in static memory use: "p;0;0x0;0x0;<ptr_addr>;;"

FIFO message (prefix 'p'):
e.g. "p0xdeadbeef"