You have a browser of one tab where you start on the `homepage` and you can visit another `url`, get back in the history number of `steps` or move forward in the history number of `steps`.

Implement the `BrowserHistory` class:

- `BrowserHistory(string homepage)` Initializes the object with the `homepage` of the browser.
- `void visit(string url)` Visits `url` from the current page. It clears up all the forward history.
- `string back(int steps)` Move `steps` back in history. If you can only return `x` steps in the history and `steps > x`, you will return only `x` steps. Return the current `url` after moving back in history at most `steps`.
- `string forward(int steps)` Move `steps` forward in history. If you can only forward `x` steps in the history and `steps > x`, you will forward only `x` steps. Return the current `url` after forwarding in history at most `steps`.

Example:

    Input:
    ["BrowserHistory","visit","visit","visit","back","back","forward","visit","forward","back","back"]
    [["leetcode.com"],["google.com"],["facebook.com"],["youtube.com"],[1],[1],[1],["linkedin.com"],[2],[2],[7]]
    Output:
    [null,null,null,null,"facebook.com","google.com","facebook.com",null,"linkedin.com","google.com","leetcode.com"]

    Explanation:
    BrowserHistory browserHistory = new BrowserHistory("leetcode.com");
    browserHistory.visit("google.com");       // You are in "leetcode.com". Visit "google.com"
    browserHistory.visit("facebook.com");     // You are in "google.com". Visit "facebook.com"
    browserHistory.visit("youtube.com");      // You are in "facebook.com". Visit "youtube.com"
    browserHistory.back(1);                   // You are in "youtube.com", move back to "facebook.com" return "facebook.com"
    browserHistory.back(1);                   // You are in "facebook.com", move back to "google.com" return "google.com"
    browserHistory.forward(1);                // You are in "google.com", move forward to "facebook.com" return "facebook.com"
    browserHistory.visit("linkedin.com");     // You are in "facebook.com". Visit "linkedin.com"
    browserHistory.forward(2);                // You are in "linkedin.com", you cannot move forward any steps.
    browserHistory.back(2);                   // You are in "linkedin.com", move back two steps to "facebook.com" then to "google.com". return "google.com"
    browserHistory.back(7);                   // You are in "google.com", you can move back only one step to "leetcode.com". return "leetcode.com"

Constraints:

- `1 <= homepage.length <= 20`
- `1 <= url.length <= 20`
- `1 <= steps <= 100`
- `homepage` and `url` consist of '.' or lower case English letters.
- At most `5000` calls will be made to `visit`, `back`, and `forward`.