Define a major mode for the GobGen buffer

[gergelypolonkai]

Original idea from @purcell in the MELPA recipe PR.

You might consider defining a major mode to simplify setup of the widgets window: you've got code in the gobgen function such as (kill-all-local-variables) and (use-local-map widget-keymap) which would be generated automatically by define-derived-mode. So you'd have code like

(define-derived-mode gobgen-mode special-mode ...)

and then instead of widget-keymap you'd use the generated gobgen-mode-map.

Let’s define a major mode for the GobGen buffer, with some keymaps for at least the three buttons!