Menu improvements

[curiousdannii]

From i7/kerkerkruip#13

I'd like to make some improvements to Menus. Some would be appropriate to be kept in the standard I7 extension, others might be better as add-on extensions (or perhaps they could be turned on with a use option.)

Core extension:

• Add back blank line(s) at top of menu like I6 menus have
• Proportional text in menus
• Numerical menus
• Accept more keys to go back from a text page
• Support menus longer than a page is long
• Hint system compatible with Emily's Menus

Glulx interface possibilities:

• Consider Erik's code to hide rather than empty the main window
• Hyperlinks in menus
• Add code to vertically align menus to the top in Gargoyle
• Proportional text in status line (might not happen due to Gargoyle not supporting enough text style hints)