Make `tape` behave more like node `assert`.

This removes excess methods on the `Test` prototype.

There are a bunch of methods and aliases on the `Test` prototype
   that are not defined on assert for node core.

This adds a bunch of undocumented complexity and unnecessary
   deviation in the way that `tape` is used.

I'd be nice to remove these aliases and make `tape` a drop in
   replacement for `assert`.

This means that tape tests are more consistent and it means 
    it's easier to find the documentation by just reading the
    the node assert documentation.

This is a breaking change. Recommended version **major**.

cc @substack.