Improve boolean handling

In library there is this code:

   def set_ignore_implicit_angular_wait(self, ignore):
        if not is_boolean(ignore):
            raise TypeError("Ignore must be

But it might be better to use Robot Framework or SeleniumLibrary is_truthy method to improve boolean handling. SeleniumLibrary method is in here: https://github.com/robotframework/SeleniumLibrary/blob/master/src/SeleniumLibrary/utils/types.py
And it has been there since 3.0 release.

SeleniumLibrary boolean handling is explained in here: http://robotframework.org/SeleniumLibrary/SeleniumLibrary.html#Boolean%20arguments

I can provide you a pull request to fix the problem. Should I copy paste the implementation or can I use method from the SeleniumLibrary? If I can, it will raise minimum required SeleniumLibrary to 3.0.

Issue に示されている set_ignore_implicit_angular_wait メソッドから始め、次に SeleniumLibrary の types.py と boolean 引数のドキュメントを読んでください。サポートされている boolean 値と、プロジェクトで SeleniumLibrary 3.0 を使用できるかを確認してください。この設定が意図した boolean 形式を受け入れ、無効な値を一貫して拒否すれば完了です。