add examples for eachk

Author: rwtolbert

examples/eachk.janet

@@ -0,0 +1,13 @@
+# keys for tuple/array are 0-based index
+# prints 0 1 2 3 4
+(eachk i [1 2 3 4 5] (prin i " "))
+
+# prints 0 1 2 3 4
+(eachk i @[1 2 3 4 5] (prin i " "))
+
+# keys table/struct, but maybe not in order
+# prints :b :a
+(eachk k {:a 1 :b 2} (prinf "%v " k))
+
+# prints :foo :bar
+(eachk k @{:foo "A" :bar "B"} (prinf "%v " k))