Drop the HP reference and rephrase the "why the name" section, mention
that packagers may want the generic profile

This is needed so submodules can be built.

This isn't guaranteed, and caused issues when we assumed
incorrectly.

Credit goes to Alexander Mikhaylenko

Instead of going to an empty state, just close the window.

This gives tabs relationships and smart closing.

We need to do this to close the pages instead of
manually destroying the widget.

Gets rid of a critical error when closing the window.

Update API to use page-attached and page-detached.

Inital port away from GtkNotebook, still a lot (e.g. close button) to do

Hopefully avoid confusion with HdyTabPage

It's supposed to be 80x24, but instead it's 99x22 with default font.

Measure it again.