Auto-generate ending/start next line when typing Valadoc.

[nielsdg]

After typing the start of a valadoc comment /**, followed by an Enter, it would come in very handy to:

1. Have the next line automatically start with *
2. Have the ending */ auto-generated

[arrufat]

I don't know if this functionality should be implemented into the plugin itself since your points:

1. it is already the case for me, maybe due to tcomment
2. if you use UltiSnips, I've added a snippet to do this: just type doc<TAB> or docall<TAB>