Add *line* and *column*

[arrdem]

Fixes #51

This changeset adds the dynamic variables clojure.core/*line* and
clojure.core/*column*. These variables are bound to be the line/column
of the top level form currently being compiled and evaluated. That is
the scope of a binding of these vars is the macroexpansion and
evaluation of that top level form.

So, for instance:

;; fn decl, does nothing
(defn foo []
  (printf "Debugging... %s:%d:%d\n" *file* *line* *column*))

;; top level form
(foo)
;; compiles to
;; (.invoke (fn* [] (foo)))
;; evaluates with *line* 5, *column* 0
;; prints "Debugging... NO_FILE:5:0\n"

These Vars are handy for generating warning messages eg. in the ns
macro which refer to the line, column and file of the top level form as
well as in writing debugging macros which otherwise have to use form
metadata introspection to extract this information which could be easily
exposed.