Procedure arity introspection

http://larceny.ccs.neu.edu/doc/user-manual.html#id2536543
http://www.gnu.org/software/mit-scheme/documentation/mit-scheme-ref/Arity.html
http://docs.plt-scheme.org/reference/procedures.html
http://practical-scheme.net/gauche/man/gauche-refe_54.html#SEC96
http://ironscheme.codeplex.com/Wiki/View.aspx?title=Procedures
http://ccrma.stanford.edu/software/snd/snd/s7.html

Not able to find docs for Chez, Bigloo, Ikarus, Kawa, SCM, Gambit,
STklos, SigScheme.

IronScheme
----------

(procedure-arity proc)
Returns multiple values for the procedure arities. 

s7
--

procedure info

procedure-source, procedure-arity, procedure-documentation, and help
provide a look into a scheme function. procedure-documentation returns
the documentation string associated with a procedure (the initial
string in the function's body). procedure-arity returns a list
describing the argument list of a function: '(required-args
optional-args rest-arg). procedure-source returns the source (as a
list) of a procedure.

    > (define* (add-2 a (b 32)) "add-2 adds its 2 args" (+ a b))
    add-2

    > (procedure-documentation add-2)
    "add-2 adds its 2 args"

    > (procedure-arity add-2)
    (0 2 #f)

    > (procedure-source add-2)
    (lambda* (a (b 32)) "add-2 adds its 2 args" (+ a b))