Rename the value-getting subs to value()

[masak]

Currently,

int(Q::Literal::Int(42));            # 42
str(Q::Literal::Str("Bond"));        # "Bond"
array(Q::Literal::Array([1, 2]));    # [1, 2]

At the time, I thought it kind of cute that we could re-use int and str as both coercers and destructors. Now it feels like the "cute today" kind of cute, though. (For some value of "today" in the past.)

I'd like to rename all these to value() instead. Reasons:

• It's clearer what that actually does
• It puts all literals under a unified interface, kind of (even Q::Literal::None!)
• It looks better when written as method calls