Remove recursion from Delaunator::legalize

[delfrrr]

data controlled recursions can case stack overflows
cc @cleeus

[flippmoke]

Recursion is often a valid design philosophy, I am not quite sure why you removed it @delfrrr -- is there some particular case it was often failing?

[delfrrr]

well, as I understand uncontrolled recursion can case stack overflows, as it stated earlier, plus it will create and keep more variables comparing to current implantation;

[flippmoke]

I reverted back to recursion in my restructured design test (that started before this landed) in #14. I am going to think about how to remove it, but the extra initialization of a vector seems to be rather heavy and might cause even more allocations. There is no reason as well that this vector couldn't grow in endlessly in size (just like your stack) in the event of an endless loop.