BUG: Clearing a `Styler` should clear all
Currently `Styler.clear()` will clear the styles built up with the `apply` `aaplymap` and `where` method. It will clear class from the `set_td_classes` method and it will clear tooltips set with `set_tooltips`.

It does not clear table styles, and it does not clear formats. It does not reset hidden index or hidden columns.

Thoughts and PR into what this should do and how it should it be documented, as well consistency with `Styler.copy` are welcome..