Introduce the --trace=actions option

[ydah]

The concept of merging actions was born in Inline. I think it would be useful to have an option to print the resolved action. However, we don't know what it is when I just display the action, so I've decided to print the rule and its corresponding action like this:. What do you think?

❯ exe/lrama --trace=actions sample/calc.y
Grammar rules with actions:
$accept -> list, YYEOF {}
list -> ε {}
list -> list, LF {}
list -> list, expr, LF { printf("=> %d\n", $2); }
expr -> NUM {}
expr -> expr, '+', expr { $$ = $1  +  $3; }
expr -> expr, '-', expr { $$ = $1  -  $3; }
expr -> expr, '*', expr { $$ = $1  *  $3; }
expr -> expr, '/', expr { $$ = $1  /  $3; }
expr -> '(', expr, ')' { $$ = $2; }

[yui-knk]

LGTM, thank you!