util/stack: extend stack api with r_stack_size
core/graph: use RStack instead of a custom implementation
util/graph: change implementation to use lists and extend api
core/cmd_debug: avoid free r_graph_get_nodes
core/graph: rename some functions and use typedefs for graph struct
core/graph: use RGraph for the ascii art graph
util/list: add const whenever possible
util/graph: add const on r_graph_get_nodes/neighbours
core/graph,core/cmd_debug: use const
core/graph: clean the code (add comments, use const, remove magic nums)
* use r_graph_node_iter for the current node
* reset graph when reloading nodes
* on callgraph edges printing, nth should be 0
* force seek of current node when reloading nodes
* use graph_foreach_node
* core/graph: remove get_current_node because useless
