Add deref and @ shortcut to more places

[jafingerhut]

For example, for atoms, delays, futures, and promises, Agent/examine.

The doc string for deref mentions @var. One normally never needs deref/@ for a var, right? Why is it there? Wow, I can't believe I didn't know this about Clojure before:

user=> (def y 7)

'user/y

user=> y
7
user=> (class y)
java.lang.Long
user=> (def x (var y))

'user/x

user=> x

'user/y

user=> (class x)
clojure.lang.Var
user=> @x
7