copy from 05_wizards_game.scm

next is start 06_wizards_game
finito 06_wizards_game
start 07_graph_util

add dot-name function
add dot-label function
add gitignore

because except *.swp
modify gitignore

because except *.dot, *.dot.png
add nodes->dot function
add edges->dot function
add graph->dot function
add dot->png, graph->png function
add ugraph's function
finito 08_grand_theft_wumpus
start 09_orc_battle