Support two argument at-irrational

[LilithHafner]

@irrational logten 2.302585092994046 log(big(10))
# can now become
@irrational logten log(big(10))

Needs tests; I'll add them if folks think this is a good idea.

[simeonschaub]

We definitely don't want to call eval inside a macro. Why not:

Suggested change

	irrational(sym, Float64(eval(def)), def)
	irrational(sym, :(Float64($def)), def)

[JeffBezanson]

Yes this would be better, but still has the problem of potentially allocating a new BigFloat each time Float64(::Irrational) is called. In this case the macro should generate a let binding for the value around those method definitions.

[LilithHafner]

I still don't totally understand macro programming, but when I tested @simeonschaub's suggestion I got

ERROR: MethodError: no method matching Float32(::Expr)

[LilithHafner]

I think I've figured it out and implemented what @JeffBezanson recommended.

[LilithHafner]

I don't think the @irrational macro is currently tested at all (grep -r @irrational test), and I'm not sure how to write a test for it. I'd appreciate advice.

[KristofferC]

Should the existing @irrational usages switch to this form now?

[LilithHafner]

Bump

[LilithHafner]

Bump. Is there anything else this needs?