Inconsistent method names

[jtpalmer]

SDLx::Widget::Menu has method event_hook

SDLx::Widget::Textbox has method event_handler

These methods both have the same use case. We should probably pick one of name and stick with that.

[jtpalmer]

After another look, it might make sense to make event_hander a private method for the textbox.

[FROGGS]

You are right, that Textbox::event_handler should be private.