Printing the values of variables should be optional

[vsajip]

If I do at the gore> prompt

some_var, err := some_func()

the values of some_var and err are always printed. Can this be made optional? If I want to type more than one command when exploring some library, for example, I don't necessarily want to clutter the display with all elements of returned structures. Of course, typing the name of a variable should display the value, as it does currently - it just shouldn't perhaps print automatically on assignments. This is related to #139, I guess.

[itchyny]

This would be a new command line flag.

[vsajip]

Yes - or more flexibly, perhaps, a new :-command such as :verbose that the user could invoke multiple times in a gore session, working as a toggle, or else taking an argument such as :verbose on / :verbose off.