Merge pull request #285 from rwtolbert/example_eachk

add examples for eachk

examples/eachk.janet

@@ -0,0 +1,13 @@
+# keys for tuple/array are 0-based index
+# prints 0 1 2 3 4
+(eachk i [:a :b :c :d :e] (prin i " ")) # -> nil
+
+# prints 0 1 2 3 4
+(eachk i @["a" "b" "c" "d" "e"] (prin i " ")) # -> nil
+
+# prints keys in table/struct in an unspecified order
+# prints :b :a
+(eachk k {:a 1 :b 2} (prinf "%v " k)) # -> nil
+
+# prints :foo :bar
+(eachk k @{:foo "A" :bar "B"} (prinf "%v " k)) # -> nil