[WIP] Add ability to parse parts of json

[DeLaGuardo]

New core function to parse parts of json from the stream (potentially large one)

(parse-stream rdr nil nil [#{"some"} #{"nested"} #{"attributes"}])
(parse-stream rdr nil nil [#{:using} #{:key-fn}] true)

Few more tests added to track the performance.

Right now parts can be retrieved by the path passed as a set of predicates as a second argument.

Lazy seq will return when the path points to the key which contains the array and argument detach-children? is true.

;; {"foo": [{"bar": 1}, {"bar": 2}]}
(take 1 (parse-stream rdr nil nil [#{"foo"}] true))
;; => ({"bar" 1})

And you can continue the path after array pointer to return partial objects from array as lazy seq.

(def jstr "{\"foo\": [{\"bar\": 1}, {\"bar\": 2, \"baz\": 3}]}")
(def x (parse-string jstr nil nil [#{"foo"} #{"bar"}] true))
(type x) ;; => clojure.lang.LazySeq
(second x) ;; => {"bar" 2}

As you can see it works with parse-string as well (and with all other public functions)

Should fix #62

TODO:

• consider to use jsonPath to build a list of predicates from the string