Way to Iterate Through History

As far as I can tell, linenoise does not provide a way to read lines in history via its API. I think this would be useful. I think a way to implement this could be to allow `history` to be iterated on.

perhaps something like...

```c
struct HistoryIter {
char ** history; // a pointer to the history, same type as history itself (perhaps the same reference or a copy)
int count; // the number of lines in history
}

struct HistoryIter linenoiseGetHistory();

```

or maybe a macro...

```c

char * line;
LINENOISE_HISTORY_FOREACH_LINE(line) {
...
}
```