Allow using yesno() as a context manager

[phodge]

When setting up a new system, my HOMELY.py asks if I want to install things using yesno() prompts, but then fails with a traceback because the things isn't available via the system package manager.

It'd be nice if yesno() could be used as a context manager like this:

@yesno("Install ack?")
def install_ack():
    installpkg(brew="ack")

The new behaviours you would get with this arrangement are:

• The question name is taken from the decorated function instead of the first arg
• If the decorated function raises an exception, the traceback is logged, the saved answer is reset (so you have to decide Y/N next time)
• script execution continues

The benefits are:

• If something fails, the whole script doesn't come to a halt
• You don't have to use -a and answer every question again to disable one thing that was broken