Add feature to export NFA/DFA table as state diagram

[SicroAtGit]

For this feature the tool Graphviz will be used and should replace these codes:

• examples/Debug_NFA_table.pb
• examples/Debug_DFA_table.pb

For example, the regex engine creates the following dot code for the regex (a|b):

digraph nfa_state_diagram {

	rankdir = LR;
	size = "8,5";
	node [shape = circle];
	"" [shape = none, fixedsize = true, height = 0, width = 0];

	"" -> 1;

	1 -> 2 [label = "ε", style = dashed];

	2 -> 3 [label = "61"];

	3 -> 4 [label = "00"];

	4 -> 5 [label = "ε", style = dashed];

	5 [shape = doublecircle];

	1 -> 6 [label = "ε", style = dashed];

	6 -> 7 [label = "62"];

	7 -> 8 [label = "00"];
	
	8 -> 5 [label = "ε", style = dashed];
}

Graphviz then generates this NFA diagram visualization from the dot code:

[tajmone]

This feature is really cool, but I suggest that you pack it into an extra optional module instead of the native library, because the native PB compiler doesn't optimize for dead code, which means that the code for the graphs would be included in the generated binary file even in applications that don't actually use it.

GCC does remove dead code from the final binary, but since we don't know the internals of the PB-GCC backend we can't be sure of this without experimenting whether this optimization is actually enforced.